Review of DNA and Chromosomes
Our DNA wind up neatly into a CHROMOSOME.
Chromosomes contain alleles. Alleles are specific gene clusters on a chromosome.
Review of DNA and Chromosomes There are 46 individual chromosomes in a
human cell. When a person wants to reproduce, half the chromosomes are passed on. 23 from mom 23 from dad
Homologous pair
Inheritance of chromosomes Egg + sperm zygote
egg
sperm
zygote
fertilizationmitosis &
development
meiosis
Inheritance of genes After fertilization, you now have a
chromosome from each parent. Alleles (genes) may have same information Alleles may be different information
eye color(blue or brown?)
eye color(blue or brown?)
Inheritance of genes
Alleles are inherited separately from each parent Let’s say you have one allele for brown eyes &
one allele for blue eyes. The colors are separate & do NOT blend
either have brown or blue, no blend
Some alleles mask others brown eye color masked blue brown is dominant
Genes Dominant Gene – The gene that is
expressed Illustrated by a capitol letter
Recessive Gene – The gene that is hidden Illustrated by a lower case letter
Genes If both parents give you the same
gene, we call it homozygous. Purebred Example – Two blue eye genes (bb)
Genes If parents give you two different genes on
the alleles, we call it heterozygous. Hybrid Example – a brown and a blue (Bb) BUT….which of the two traits will be
expressed?
Punnett Squares
To determine the odds of that traits might be passed on to the offspring, we can do Punnett Square.
To do a Punnett Square, you have to know what alleles the parent has. In our example, we will cross two heterozygous
people. (Bb)
Genetics vs. appearanceThere can be a difference between
how an organism looks & its geneticsappearance or trait = phenotype
brown eyes vs. blue eyesgenetic makeup = genotype
BB, Bb, bb
2 people can have the same appearance but have different genetics: BB vs Bb
Genetics vs. appearance
eye color(brown B)
eye color(brown B)
eye color(blue b)
eye color(brown B)
vs.
BB
B
BBb
B
b
How were these brown eyes made?How were these brown eyes made?
Karyotype
A kayrotype is the number and visual appearance of the chromosomes in the cell nuclei of an organism or species.
By studying karyotypes, you can determine what traits are
inherited.
In other words…
Chromosomes are digitally arranged so that they are matched with their homologue or “partner” chromosome.
Homologue chromosomes are the same size, shape, and carry the same genes, and one is inherited from each parent.
They are numbered according to size.
Sex determination with karyotype This karyotype has 23
exact pairs.
Note that #23 chromosomes are both X. Therefore this is a female.
Trisomy 21 Abnormality
shown in karyotype
Note that there are three copies of #21 chromosome.
This person has Down Syndrome.
Monosomy X Abnormality
shown in karyotype
Note this person only has 1 copy of the X chromosome.
This female has Turner’s syndrome.
XXY Male (Extra X) Abnormality
shown in karyotype
Note this person has 3 sex chromosomes.
This male has Klinefelter's Syndrome.
If there are chromosomal number abnormalities, how do they form? Meiosis: the process of creating sperm or
egg from a diploid cell
If there is a mistake when chromosomes are separating, then the resulting sperm or egg will have too many or too few chromosomes.