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Basic Genetic Concepts & Terms & Punnett Squares
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Chapter 2.2 - Heredity and Genetics
Genetics: what is it?
What is genetics? What is genetics? ““Genetics is the study of Genetics is the study of heredityheredity, the process in which a , the process in which a
parent passes certain parent passes certain genes genes onto their children.”onto their children.”
What does that mean?What does that mean? Children Children inheritinherit their biological parents’ genes that their biological parents’ genes that
express specific express specific traitstraits, such as some physical , such as some physical characteristics, natural talents, and genetic disorders. characteristics, natural talents, and genetic disorders.
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Word Match Activity
Match the genetic terms to Match the genetic terms to their corresponding parts their corresponding parts of the illustration.of the illustration.
Handout Word Match WSHandout Word Match WS• base pairbase pair• cellcell• chromosomechromosome• DNADNA
(Deoxyribonucleic Acid)(Deoxyribonucleic Acid)• *double helix*?*double helix*?• genesgenes• nucleusnucleus
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Word Match Activity• base pairbase pair• cellcell• chromosomechromosome• DNADNA
(Deoxyribonucleic Acid)(Deoxyribonucleic Acid)• double helix*double helix*• genesgenes• nucleusnucleus
Illustration Source: Talking Glossary Illustration Source: Talking Glossary of Genetic Terms of Genetic Terms http://www.genome.gov/glossary.chttp://www.genome.gov/glossary.cfm?key=chromosomefm?key=chromosome
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base pair
cell
nucleus chromosome
(doublehelix)DNA
genes
Genetic Concepts
HH describes how some traits are describes how some traits are passed from parents to their children.passed from parents to their children.
The traits are expressed by The traits are expressed by gg , which , which are small sections of DNA that are coded for are small sections of DNA that are coded for specific traits.specific traits.
Genes are found on Genes are found on chch ______.. Humans have two sets of Humans have two sets of __ (hint: a number) (hint: a number)
chromosomes—one set from each parent.chromosomes—one set from each parent.
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Genetic Concepts
HeredityHeredity describes how some traits are describes how some traits are passed from parents to their children.passed from parents to their children.
The traits are expressed by The traits are expressed by genesgenes, which are , which are small sections of DNA that are coded for small sections of DNA that are coded for specific traits.specific traits.
Genes are found on Genes are found on chromosomeschromosomes.. Humans have two sets of Humans have two sets of 2323 chromosomes— chromosomes—
one set from each parent.one set from each parent.
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Genetic Terms
– Allele: Allele: An allele is an alternative form of a gene (one member of a An allele is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome.pair) that is located at a specific position on a specific chromosome.
– Genes: Genes: It is a name given a part of DNA and RNA It is a name given a part of DNA and RNA
– Dominant : The stronger of the two alleles. ExpressedDominant : The stronger of the two alleles. Expressed
– Recessive: The weaker of the two alleles. HiddenRecessive: The weaker of the two alleles. Hidden
– Homozygous: Both alleles are the same.Homozygous: Both alleles are the same.
– Heterozygous: Two different alleles.Heterozygous: Two different alleles.
– Genotype: Genotype: This is the "internally coded, inheritable information" This is the "internally coded, inheritable information" carried by all living organisms. “Blueprint”carried by all living organisms. “Blueprint”
– Phenotype: Phenotype: This is the "outward, physical manifestation" of the This is the "outward, physical manifestation" of the organism.organism.
– Mendellian Inheritance: Mendellian Inheritance: A scientific theory of how hereditary A scientific theory of how hereditary characteristics are passed from parent organisms to their offspring.characteristics are passed from parent organisms to their offspring.
– HybridHybrid: A cross breeding of two purebreds. Red & White flowers.: A cross breeding of two purebreds. Red & White flowers. 7
Mendelian Inheritance
1.1. The inherited traits are determined by genes that The inherited traits are determined by genes that are passed from parents to children.are passed from parents to children.
2.2. A child inherits two sets of genes—one from each A child inherits two sets of genes—one from each parent.parent.
3.3. A trait may not be observable, but its gene can be A trait may not be observable, but its gene can be passed to the next generation. passed to the next generation.
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Mendelian Inheritance Each person has 2 copies of every gene—one copy Each person has 2 copies of every gene—one copy
from mom and a second copy from dad. These from mom and a second copy from dad. These copies may come in different variations, known as copies may come in different variations, known as allelesalleles, that express different traits. , that express different traits.
For example, 2 alleles in the gene for freckles are inherited from For example, 2 alleles in the gene for freckles are inherited from mom and dad:mom and dad: allele from mom = has freckles (F) - Dominantallele from mom = has freckles (F) - Dominant allele from dad = no freckles (f) - Recessiveallele from dad = no freckles (f) - Recessive child has the inherited gene pair of alleles, child has the inherited gene pair of alleles, Ff Ff (F allele (F allele
from mom and f allele from dad).from mom and f allele from dad).
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Punnett SquaresPunnett Squares
What is a PUNNETT SQUARE? A tool to predict the probability of A tool to predict the probability of
certain traits in offspring that shows certain traits in offspring that shows the different ways alleles can the different ways alleles can combinecombine
A way to show phenotype & A way to show phenotype & genotypegenotype
A chart that shows all the possible A chart that shows all the possible combinations of alleles that can combinations of alleles that can result when genes are crossedresult when genes are crossed
What is a PUNNETT SQUARE?
Letters stand for dominant and Letters stand for dominant and recessive allelesrecessive alleles
An uppercase letter stands for a An uppercase letter stands for a dominant allele dominant allele
Lowercase letters stand for recessive Lowercase letters stand for recessive allelesalleles
Using a PUNNETT SQUARE
To set up a Punnett square, draw a To set up a Punnett square, draw a large square, and then divide it into large square, and then divide it into 4 equal sections (also squares). It 4 equal sections (also squares). It should look something like this:should look something like this:
Using a PUNNETT SQUARENow you need two parents to mate, Now you need two parents to mate,
ones with a known genotypeones with a known genotype
For example, a red flower (genotype For example, a red flower (genotype Rr) and a white flower (genotype rr). Rr) and a white flower (genotype rr). Rr x rrRr x rr
Using a PUNNETT SQUARE
Place one of the parents on top, and Place one of the parents on top, and one on the left. You should get a one on the left. You should get a something similar to this:something similar to this:
Using a PUNNETT SQUARE
Finally, take each letter in each column and Finally, take each letter in each column and combine it with each letter from each row in combine it with each letter from each row in the corresponding square. You should now the corresponding square. You should now have a picture close to this:have a picture close to this:
Using a PUNNETT SQUARE
The two-letter combinations are the The two-letter combinations are the possible genotypes of offspringpossible genotypes of offspring
They are: Rr, Rr, rr, and rr genotypesThey are: Rr, Rr, rr, and rr genotypes From this it is possible to determine From this it is possible to determine
the probability (chance) that a flower the probability (chance) that a flower will have a red phenotype (2/4 or will have a red phenotype (2/4 or 50%) or a white phenotype (2/4 or 50%) or a white phenotype (2/4 or 50%)50%)
Mendel’s Laws of Inheritance1. Law of Dominance: In heterozygous genotypes,
dominant alleles hide recessive alleles when both are inherited by an organism. (Hh means the dominant trait will show up in the phenotype)
Mendel’s Laws of Inheritance
1. The Law of Segregation (separation): Each organism has 2 alleles for a gene. Only one allele from each gene pair will be passed on to the offspring.
Homozygous/Heterozygous
Cross a homozygous Cross a homozygous dominant tall plant dominant tall plant with a homozygous with a homozygous recessive short plant. recessive short plant.
What letters would you use to represent this cross?
Dominant trait = tall Dominant trait = tall
Recessive trait = shortRecessive trait = short
T = tall T = tall t = short t = short
Hmzg / Htzg
What is the genotype of a homozygous What is the genotype of a homozygous dominant tall plant?dominant tall plant?
GenotypeGenotype
% % TTTT
% % TtTt
% tt% tt
TT TT
TT x ttTT x tt
What is the genotype of a homozygous What is the genotype of a homozygous recessive short plant?recessive short plant? tt tt
t t
T
T
PhenotypePhenotype
% tall% tall
% % shortshort
Tt Tt
Tt Tt
0
100
0
0
100
2. Cross a heterozygous brown haired rabbit 2. Cross a heterozygous brown haired rabbit with a homozygous recessive white haired with a homozygous recessive white haired rabbit.rabbit.
o What letters would you use to represent this cross?
Dominant trait = Dominant trait = brown hairbrown hair
Recessive trait = Recessive trait =
white hairwhite hair B = brownB = brown b = whiteb = white
What is the genotype of a heterozygous What is the genotype of a heterozygous brown haired rabbit?brown haired rabbit?
GenotypeGenotype
% % BBBB
% % BbBb
% % bbbb
Bb Bb
Bb x bbBb x bb
What is the genotype of a homozygous What is the genotype of a homozygous recessive white haired rabbit?recessive white haired rabbit? bb bb
b b
B
b
PhenotypePhenotype
% % brownbrown
% % whitewhite
bb bb
Bb Bb
0
50
50
50
50
3.. Cross a homozygous dominant 3.. Cross a homozygous dominant long haired guinea pig with a long haired guinea pig with a heterozygous long haired guinea pig.heterozygous long haired guinea pig.
o What letters would you use to represent this cross?
Dominant trait = Dominant trait = long hairlong hair
Recessive trait = Recessive trait =
short hairshort hair L = longL = long l = short l = short
What is the genotype of a homozygous What is the genotype of a homozygous dominant long haired guinea pig?dominant long haired guinea pig?
GenotypeGenotype
% % LLLL
% % LlLl
% ll% ll
LLLL
LL x LlLL x Ll
What is the genotype of a heterozygous What is the genotype of a heterozygous long haired guinea pig?long haired guinea pig? Ll Ll
L l
L
L
PhenotypePhenotype
% long% long
% % shortshort
LL Ll
LL Ll
50
50
0
0
100
4. Cross a heterozygous wrinkly 4. Cross a heterozygous wrinkly elephant with another heterozygous elephant with another heterozygous wrinkly elephant.wrinkly elephant.
What letters would you use to represent this cross?
Dominant trait = Dominant trait = wrinkly skinwrinkly skin
Recessive trait = Recessive trait =
smooth skinsmooth skin W = wrinklyW = wrinkly w = smooth w = smooth
What is the genotype of a heterozygous What is the genotype of a heterozygous wrinkly-skinned elephant?wrinkly-skinned elephant?
GenotypeGenotype
% % WWWW
% % WwWw
% % wwww
WwWw
Ww x WwWw x Ww
What is the genotype of a heterozygous What is the genotype of a heterozygous wrinkly-skinned elephant?wrinkly-skinned elephant? WwWw
W w
W
w
PhenotypePhenotype
% % wrinklywrinkly
% % smoothsmooth
Ww ww
WW Ww
25
50
25
25
75
PhenotypePhenotype
% round% round
% % wrinkledwrinkled
5. A plant that is homozygous dominant for round seeds is crossed with a heterozygous plant. What is the probability that the offspring will have
wrinkled seeds?
RR x RrRR x Rr
R r
R
R
RR Rr
RR Rr
R = round
GenotypeGenotype
% % RRRR
% Rr% Rr
% rr% rr
r = wrinkled
50
50
0
0
100
