Mendel and Heredity

Mendel and Heredity Terms

• Gregor Mendel- “Father of Genetics”• Traits- characteristics that are

inherited– Ex. Eye color, hair color

• Genetics- study of biological inheritance patterns• Purebred- offspring inherit all

of parents characteristics, genetically uniform

Mendel and Heredity Terms

• Cross- mating of two organisms

• Gene- piece of DNA that provides a set of instruction to a cell

• Allele- any alternative form of a gene that may occur

Mendel and Heredity Terms

• Homozygous- two of the same alleles• Heterozygous- two different alleles

Mendel and Heredity Terms

• Genotype- genetic makeup of a specific set of genes

• Phenotype- physical characteristics or appearance of an organism

• Dominant- allele is expressed when two different alleles are present

• Recessive- allele is expressed only when two copies are present

Genetics

• In the 1800’s, Gregor Mendel laid the groundwork for modern genetics

• He crossed many pea plants and observed traits of offspring• Discovered that– Organisms inherit two copies of each gene, one from each

parent

Genetics

• Peas either:– Round (dominant)– Wrinkled (recessive)

• Genotypes Phenotypes– RR (homozygous dominant) -round– Rr (heterozygous) -round– rr (homozygous recessive) -wrinkled

Genetics

• Another example:

• Brown (dominant) vs. black (recessive)• Genotypes? Phenotypes?

Genetics

• Mendel’s discoveries led to the Punnett square

• Developed by R.C. Punnett • Used to predict genotypes of offspring• Example: – Straight (dom.) vs. curly (rec.)– Dad-heterozygous– Mom-homozygous recessive

Dihybrid Punnett Square

• Predicting more than one trait• EX. Cross a tall pea plant with green leaves

with a short pea plant with yellow leaves.1. Determine parent genotypes.2. Find combinations of alleles.3. Fill out Punnett square.4. Determine phenotypes of offspring.

Dihybrid Punnett Square• EX. Cross a tall (homozygous) pea plant with green

(heterozygous) leaves with a short pea plant with yellow leaves. (Tall is dominant to short, green is dominant to yellow)

Dihybrid Practice

• Cross the parents SsYy x SsYy

SSYY SSYy SsYY SsYy

SSYy Ssyy SsYy Ssyy

SsYY SsYy ssYY ssYy

SsYy Ssyy ssYy ssyy

SY sysYSy

sysY

SySY

Smooth/Yellow __9____Smooth/Green ___3___Rough/Yellow ____3__Rough/Green _____1_

Bellringer:Complete both questions in your notebook

• 1. In one particular species of cats, long hair is dominant to short hair. If a heterozygous male is crossed with a homozygous recessive female, what is the probability that one of the offspring has long hair?

• 2. A homozygous dominant flower is crossed with a homozygous recessive flower. Purple flowers are dominant to red flowers. What are the genotypes and phenotypes of the offspring?

Sex-linked Genes

• Sex-linked genes- genes located on the sex chromosomes– Female (XX), Male (XY)

XX XY

XX XY

X YX

X

Incomplete Dominance

• Alleles that show incomplete dominance show both the dominant and recessive traits

• Neither allele is completely dominant or recessive

• Ex. If a homozygous red flower and homozygous white flower cross, the offspring have pink flowers

Codominance

• Both the dominant and recessive alleles are expressed

• Ex. Red and white flower are crossed, the offspring will be red and white

Exit Slip

1. Sex linked genes are located ______________.

2. A dog that shows the phenotypes of both his mother and father would be an example of (incomplete or codominance).

3. A blue flower crosses with a yellow flower to produce a green flower. This is an example of (incomplete or codominance).

Pedigree

• Pedigree- chart that can help trace phenotypes and genotypes in a family– Helps to determine if people carry the recessive

allele

Pedigree

Pedigree

• Reading a pedigree

Example

○ □

□ ○ □How many boy children? How many girl children?Is the oldest child a boy or girl?

Griffith Experiment

DNA Structure

• DNA is a polymer made of monomers called nucleotides

• Each nucleotide is made of:– A phosphate group– Deoxyribose (sugar)– Nitrogen containing base

Types of Nucleotides

• C – CytosinePyrimidines

• T – Thymine

• A – Adenine Purines• G – Guanine

Base-Pairing Rules

• Nucleotides always pair in the same way– Thymine (T) always pairs with Adenine (A)– Cytosine (C) always pairs with Guanine (G) – Ex. TTACGTAG AATGCATC

DNA Structure

• DNA is in the shape of a double helix• Each nucleotide is paired

Exit Slip

1. Thymine is an example of a _____________.• nucleotide

2. The shape of DNA is known as a ___________.• Double helix

3. Write the DNA base pair:TCGGAATCCACGTG_______________– AGCCTTAGGTGCAC

DNA Replication

• Replication is a process by which DNA is copied

• Occurs during the S stage of the cell cycle