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 XYXX 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