lecture 14 complex inheritance

pedigree chart

A pedigree chart shows how a trait is inherited through a family over generations.

why are pedigree charts used?

They help determine inheritance patterns, such as whether a trait is dominant, recessive, autosomal, or sex-linked.

what do the symbols mean?

What does a circle mean in a pedigree?
A: A female.

What does a square mean in a pedigree?
A: A male.

What does a shaded symbol mean in a pedigree?
A: The individual has the trait.

What does an open symbol mean in a pedigree?
A: The individual does not have the trait.

how do you tell if a trait is x-linked?

Clues include:

• more males affected

• no father-to-son transmission for X-linked traits

• affected sons often inherit the allele from the mother

how do you determine if a trait is autosomal?

Males and females are usually affected more equally, and father-to-son transmission can occur.

If it is X-linked, what is often assumed in intro class problems?

Often it is assumed to be X-linked recessive, unless told otherwise.

If an autosomal trait is dominant, what pattern does the pedigree often show?

It usually appears in every generation.

If an autosomal trait is recessive, what pattern does the pedigree often show?

It can skip generations, and unaffected parents can have an affected child.

what is complete dominance?

Complete dominance means one allele completely masks the other in a heterozygote

In complete dominance, what phenotype goes with PP?

The dominant phenotype.

In complete dominance, what phenotype goes with Pp?

The dominant phenotype.

In complete dominance, what phenotype goes with pp?

The recessive phenotype.

What is the big idea of complete dominance?

If there is at least one dominant allele, the dominant trait shows.

what is incomplete dominance?

Incomplete dominance means the heterozygote has an intermediate or blended phenotype.

What phenotype goes with g1g1 in incomplete dominance?

one homozygous phenotype

What phenotype goes with g1g2 in incomplete dominance?

a blended/ intermediate phenotype

What phenotype goes with g2g2 in incomplete dominance?

the other homozygous phenotype

What is the big idea of incomplete dominance?

Neither allele completely masks the other, so the heterozygote looks in-between.

what is codominance?

Codominance means both alleles are fully expressed in the heterozygote.

What phenotype goes with I^A I^A?

Type A blood

What phenotype goes with I^B I^B?

Type B blood

What phenotype goes with I^A I^B?

Type AB blood

What phenotype goes with ii?

type O blood

What is the big idea of codominance?

Both alleles show at the same time instead of blending.

what is epistasis?

Epistasis is when one gene affects or masks the expression of another gene.

what is the main idea of epistasis?

One gene can hide the effect of a different gene.

what is pleiotropy?

Pleiotropy is when one gene affects multiple traits.

What is the main idea of pleiotropy?

one gene, many effects

what is multiple allelism?

Multiple allelism means a gene has more than two allele versions in the population.

does one person have more than two alleles for a gene?

No. One person still only has two alleles, but the population can have many possible versions.

What is a common example of multiple allelism?

ABO blood type

what is a polygenic trait

A polygenic trait is controlled by many genes.

What kind of variation do polygenic traits usually show?

continuous variation like a range

Give examples of polygenic traits.

height and skin color

what is multifactorial inheritance

Multifactorial inheritance means a trait is affected by both genes and environment.

In multifactorial inheritance, which is modified: phenotype or genotype?

phenotype

In multifactorial inheritance, which remains unchanged: phenotype or genotype?

genotype

what is the big idea of multifactorial inheritance?

Genes set the potential, and the environment helps shape the final trait.

What are linked genes?

Linked genes are genes located close together on the same chromosome.

how were linked genes used for mapping genes

Scientists looked at recombination frequency. If two genes recombined often, they were farther apart. If they recombined less often, they were closer together.

What is the key idea of gene mapping with linked genes?

More crossing over means the genes are farther apart on the chromosome.

what is a single gene trait?

A single-gene trait is a trait controlled mainly by one gene.

what is a multiple gene trait

A multiple-gene trait is a trait controlled by more than one gene.

What is the main difference between single-gene and multiple-gene traits?

Single-gene traits are controlled by one gene and are usually simpler to predict. Multiple-gene traits are controlled by several genes and are usually more complex.

which type is commonly used for practice with punnett squares?

Single-gene traits are commonly used with Punnett squares because they are simpler.

Why are multiple gene traits harder to predict?

Because several genes contribute to the final trait, so there are more possible combinations.

How can multiple genes impact a single trait?

• Polygenic inheritance — many genes all contribute to one trait

• Epistasis — one gene affects or masks the expression of another gene

what is a discrete trait?

A discrete trait has clear categories with no in-between.

what is a continuous trait?

A continuous trait has a range of values and can vary gradually.

What is the difference between discrete and continuous traits?

Discrete traits fall into separate groups. Continuous traits show a spectrum or range.

give an example of a discrete trait

Blood type is a discrete trait because the categories are A, B, AB, or O.

give an example of a continuous trait

Height is a continuous trait because it can vary across a range.

How do you identify a discrete trait from a description?

look for traits with distinct categories

How do you identify a continuous trait from a description?

look for traits that show a range of values

what is a wild type allele

A wild type allele is the most common version of a gene in a population.

What is a mutant allele?

A mutant allele is a version of a gene that has changed from the wild type.

Which is more common: wild type or mutant allele?

The wild type allele is more common.

which tends to be the dominant allele?

In many intro biology examples, the wild type allele tends to be dominant, though not always in every real-life case.

what is an autosomal trait

An autosomal trait is a trait controlled by a gene located on an autosome, which is a non-sex chromosome.

Where are autosomal traits located?

On the autosomes, not on X or Y.

How are autosomal traits depicted?

With regular allele letters, like A/a or B/b.

Why are autosomal traits more common?

Because most chromosomes are autosomes, so most genes are found there.

Do autosomal traits affect males and females equally?

Usually yes, because both males and females have autosomes.

What is a sex-linked trait?

A sex-linked trait is controlled by a gene on a sex chromosome, usually the X chromosome.

Where are sex-linked traits located?

on the X or Y chromosome

How are sex-linked traits depicted?

By writing the allele on the chromosome, like X^A, X^a, or Y.

Why are males impacted more often by X-linked traits?

Males have only one X chromosome, so if that X has a recessive allele, the trait is expressed.

Why are females less often affected by X-linked recessive traits?

Females have two X chromosomes, so one dominant allele on one X can hide a recessive allele on the other.

What are two examples of X-linked traits?

colorblindness and hemophilia

Who can be impacted by a Y-linked trait?

Only males, because only males have a Y chromosome

How is a Y-linked trait passed?

from father to son

What is a sex-influenced trait?

A sex-influenced trait is usually an autosomal trait whose expression is affected by the sex of the individual.

Where are sex-influenced traits located?

Usually on the autosomes, not the sex chromosomes.

How are sex-influenced traits different from most autosomal traits?

The same genotype may be expressed differently in males and females.

How are sex-influenced traits different from sex-linked traits?

Sex-influenced traits are on autosomes. Sex-linked traits are on sex chromosomes.

what is a karyotype?

A karyotype is an organized picture of chromosomes arranged in pairs by size and shape.

how do we use a karyotype

To examine chromosome number, sex chromosomes, and chromosome abnormalities

What are autosomes in a karyotype?

The non-sex chromosomes, pairs 1 through 22 in humans.

What are sex chromosomes in a karyotype?

The chromosomes that determine sex: X and Y.

How do you identify a female from a karyotype?

XX

How do you identify a male from a karyotype?

XY

How do you identify chromosomal abnormalities in a karyotype?

Look for missing chromosomes, extra chromosomes, or unusual chromosome structure.

What is an example of a chromosomal abnormality?

Trisomy 21, which causes Down syndrome.