Biology Genetics Unit

Gregor Mendel Considered the father of modern genetics He was an Austrian monk in the mid 1800’s He did many experiments with pea plants

Mendel Continued He discovered the basics for genetics as we know it today In the following slides, we will cover his major discoveries

Dominant Traits In a pair of traits, this one always has an effect These traits get represented with a capital letter (B)

Recessive Traits A trait that is only seen when two copies of the gene are present

Alleles Different forms of the same trait or gene Examples would be blue and brown eyes, or hitchhikers and straight thumbs

Homozygous A term describing an organism that has two of the same genes This could be two dominant traits (BB) or two recessive traits (bb)

Heterozygous A term describing organisms that have two different genes for a trait. This means they have one dominant and one recessive trait (Bb)

Genotype The genes that an organism has for a trait. For example, attached earlobes are a recessive trait, so a person with them must have two copies of that trait. Therefore, their genotype is “ee.”

Phenotype This is the actual, physical trait that a person has. For example, if a person has the genes “Ee” for earlobe shape, their phenotype will be the dominant trait, which is free earlobes.

Incomplete Dominance Sometimes, one trait does not dominate the other, and both the dominant and recessive traits are seen.

Codominance With some traits, there can be more than one dominant allele. A good example is blood type. Type O is recessive, but types A and B are both dominant.

Punnett Squares Punnett Squares are charts that are made in order to predict the results of two organisms reproducing. Usually only one or two traits are analyzed at a time.

Single Trait Punnett Square The Problem: Brown eyes are dominant and blue eyes are recessive. Cross a heterozygous woman with a homozygous recessive male. Step 1 – define letters to represent the traits B – brownb – blue Step 2 – write down Mom and Dad’s genotypes Mom Dad Bb bb

Single Trait Punnett Square Now make the chart and put Mom and Dad’s genes on the chart.

Single Trait Punnett Square Now, bring the genes across and down to determine the genes the possible offspring will have.

Two Trait Punnett Square In this problem we will look at two traits at the same time. Problem – make a Punnett Square using the following combinations of genes. MomDad AaBb AABb

Two Trait Punnett Square Now, find the combinations of genes Mom and Dad can pass on. Mom - AaBb Dad - AABb AB AB Ab Ab aB AB ab Ab

Two Trait Punnett Squares Now, take those traits and put them on a chart.

Two Trait Punnett Squares Finally, fill in the boxes.

Sex-Linked Punnett Squares These are traits that are only found on the “X” chromosome. Females have “XX” and males have “XY” The X chromosome is very large and the Y is very small. Because of this, there is not enough room on the Y for all of the genes on the X.

Sex-Linked Punnett Squares The Problem – Color blindness is a sex-linked recessive trait. Normal vision is dominant. Cross a heterozygous woman with a man who has normal vision. Step 1 – assign letters to the trait B – normalb – color blind

Sex-Linked Punnett Squares Step 2 – add genes to Mom and Dad’s X chromosomes MomDad XBXbXBYXBXbXBY

Sex-Linked Punnett Squares Now, add Mom and Dad’s genes to the chart.

Sex-Linked Punnett Squares Finally, fill in the squares on the chart.

Pedigree Charts Pedigrees show the occurrence of specific genetic traits in a family. Each generation is designated by a Roman numeral Females are circles and males are squares When possible, the oldest person in a generation goes on the left. As you go to the right, the people should get younger.

Pedigree Charts In the chart below, the man and woman are connected by a horizontal line. This means they are married.

Pedigree Charts The vertical line dropping from the marriage line indicates children being born.

Pedigree Charts Marriages in generation II are shown below. A first marriage is always shown to the left, the second to the right.

Pedigree Charts Children are then added and generation III is formed. Note how twins are shown.

Pedigree Charts People with the recessive trait are shaded and a key is added to explain the traits.

Pedigree Charts Finally, genotypes are added to the chart.