Unit 5- Topics 4-6 AP Biology

Non-Mendelian Genetics

Why do many traits not follow the ratios predicted by Mendel’s Laws?

Varying degrees of dominance, many traits are produced through multiple genes acting together, some traits are determined by genes on the sex chromosomes, some genes are adjacent or close to one another on the same chromosome and will segregate as a unit, some traits are the result of non-nuclear inheritance (i.e. chloroplast and mitochondrial DNA)

What kind of dominance in traits was used in Mendel’s experiment?

Complete Dominance

Complete Dominance

Homozygous dominant and heterozygous individuals are phenotypically the same

Incomplete Dominance

Neither allele is fully dominant → F1 Generation has a phenotype that is a mix of those of the parental generation

Flower Example of Incomplete Dominance

Red flowers crossed with white flowers will produce pink offspring

Codominance

Two alleles that affect phenotype are both expressed (Ex: Type AB Blood)

Multiple Alleles

Genes that exist in forms with more than two alleles (Ex: human blood group)

Epistasis

The phenotypic expression of a gene at one locus affects a gene at another locus

Coat Color in Mice: Multiple Genes Example

One gene codes for pigment and a second gene determines whether or not that pigment will be deposited in the hair

Polygenic Inheritance

The effect of two or more genes acting on a single phenotype (Ex: height, human skin color)

Who experimented with fruit flies and determined that specific genes can be carried on sex chromosomes?

Thomas Hunt Morgan

Sex-Linked Gene

A gene located on either the X or the Y chromosome

Y-Linked Gene

Genes specifically found on the Y chromosome → there are very few Y-linked genes so very few disorders

X-Linked Genes

Genes found on the X chromosome

Who can fathers pass their X-linked alleles to?

All of their daughters but none of their sons

Who can mothers pass their X-linked alleles to?

Both daughters and sons

If an X-linked trait is due to a recessive allele when will females express the trait?

They are homozygous

When will males express the trait?

Since they only have one X chromosome, they will express it if they inherit it from their mother

What are examples of X-linked disorders?

Duchenne Muscular Dystrophy, Hemophilia, Color Blindness

What does the inactive X in each cell of a female condense into?

A Barr Body

What does a Barr Body help with?

Helps to regulate gene dosage in females

Genetic Recombination

Production of offspring with a new combination of genes from parents

Parental Types

Offspring with the parental phenotype

Recombinants

Offspring with phenotypes that are different from the parents

Linked Genes

Genes located near each other on the same chromosome that tend to be inherited together

Due to what do meiosis and random fertilization generate genetic variation in offspring?

Independent assortment of chromosomes, crossing over in Meiosis I, any sperm can fertilize any egg

What do linked genes show in offspring at higher than 50%?

Parental Phenotypes

What happens during crossing over?

Chromosomes from one paternal chromatid and one maternal chromatid exchange corresponding segments

What helps explain why some linked genes become separated during meiosis?

Crossing Over

What happens to the probability and frequency the further apart two genes are on the same chromosome?

The probability that a crossing over event will occur between them gets higher and the recombination frequency gets higher

Experiments performed by who allowed scientists to map genes and their locations on chromosomes?

Sturtevant

Linkage Map

Genetic map that is based on recombination frequencies

Map Units

The distance between genes which express the relative distances along chromosomes

What is one map unit equivalent to?

1% recombination frequency

What does 50% recombination mean?

That the genes are far apart on the same chromosome or on two different chromosomes

Where are some traits located on DNA found in?

Mitochondria or Chloroplasts

What similar between chloroplasts and mitochondria?

They are randomly assorted to gametes and daughter cells

In animals, what are mitochondria transmitted by?

The egg, not the sperm → All mitochondrial DNA is maternally inherited

In plants, where are mitochondria and chloroplasts transmitted through?

The ovule, not the pollen → Both mitochondrial and chloroplast determined traits are maternally inherited

Chi-Square

a form of statistical analysis used to compare the actual results (observed) with the expected results

What do chi-squares help with?

• Determines whether the data obtained experimentally provides a “good fit” to the expected data

• Determines if any deviations from the expected results are due to random chance alone or to other circumstances such as data collection error

• Designed to analyze categorical data

What is the Chi Square equation used to test?

The “null” hypothesis → The prediction that data from the experiment will match the expected results

What is the formula for Chi Square?

Sum of ((observed results-expected results)²/expected results)

Know How to Solve for Chi Square Value!!

I will <3