Biology- Inheritance

What is a genotype?

An organism’s genetic makeup; its set of genetic material

What does "genotype" refer to?

The alleles an individual possesses for a trait.

How can you remember genotype?

"Geno" sounds like genes.

What is a phenotype?

The observable characteristics of an organism.

Give examples of phenotypes.

Blue eyes, brown eyes, curly hair, attached earlobes

What determines phenotype?

The interaction between genotype and the environment.

How can you remember phenotype?

"Ph" = physical characteristics.

What is an allele?

A variation or alternative form of a gene.

How do alleles differ from one another?

By one or a few DNA bases in the gene sequence.

What are examples of eye-colour alleles?

Brown, blue, green, and grey.

What are examples of hair-colour alleles?

Blonde, red, brown, and black.

What is a dominant allele?

An allele that is expressed whenever it is present.

What is a recessive allele?

A non-dominant allele that is only expressed when two copies are present.

When is a recessive trait expressed?

When an individual inherits two recessive alleles.

If a person inherits one dominant and one recessive allele, which trait is shown?

The dominant trait.

If a person inherits two dominant alleles, which trait is shown?

The dominant trait.

If a person inherits two recessive alleles, which trait is shown?

The recessive trait.

In the second toe example, which trait is dominant?

A second toe shorter than the big toe.

In the second toe example, which trait is recessive?

A second toe longer than the big toe.

How are dominant alleles represented?

By a capital letter (e.g., R).

How are recessive alleles represented?

By a lowercase letter (e.g., r).

Which allele is written first in a genotype?

The dominant allele.

How is the letter for an allele usually chosen?

From the name of the dominant trait.

Why should allele letters be easily distinguishable?

To avoid confusion between uppercase and lowercase forms.

What does homozygous mean?

Having two identical alleles for a gene.

What is homozygous dominant?

Two dominant alleles (e.g., RR).

What is homozygous recessive?

Two recessive alleles (e.g., rr).

What does heterozygous mean?

Having two different alleles for a gene (e.g., Rr).

What phenotype does a heterozygous individual show?

The dominant phenotype.

What is complete dominance?

When a dominant allele completely masks a recessive allele.

What is autosomal inheritance?

Inheritance of genes located on non-sex chromosomes (autosomes).

What is a monohybrid cross?

A genetic cross involving one gene.

What is a Punnett square?

A diagram used to predict offspring genotypes and phenotypes.

What does a Punnett square help determine?

The probability of specific genotypes and phenotypes.

What is the first step in making a Punnett square?

Write the possible parental alleles around the square.

What is the second step?

Fill in offspring genotypes inside the square.

What is the third step?

Determine offspring phenotypes.

What happens when a heterozygous individual is crossed with a homozygous recessive individual?

50% heterozygous, 50% homozygous recessive.

What phenotype ratio results from Heterozygous × Homozygous Recessive?

50% dominant, 50% recessive.

What genotype ratio results from Heterozygous × Heterozygous?

25% homozygous dominant, 50% heterozygous, 25% homozygous recessive.

What phenotype ratio results from Heterozygous × Heterozygous?

75% dominant, 25% recessive (3:1).

What genotype ratio results from Homozygous Dominant × Homozygous Recessive?

100% heterozygous.

What phenotype ratio results from Homozygous Dominant × Homozygous Recessive?

100% dominant.

What are sex-linked traits?

Traits controlled by genes located on sex chromosomes.

Which chromosome carries most sex-linked traits?

The X chromosome.

Why are X-linked traits more common than Y-linked traits?

The X chromosome contains many more genes.

What does the Y chromosome mainly carry?

Genes for male secondary sex characteristics.

What is an X-linked trait?

A trait caused by a gene on the X chromosome.

What is a Y-linked trait?

A trait caused by a gene on the Y chromosome.

What are X-linked disorders?

Genetic disorders caused by mutations in genes on the X chromosome.

Are most X-linked disorders dominant or recessive?

Recessive.

Why are males more likely to express X-linked recessive disorders?

They have only one X chromosome.

What is a carrier?

A heterozygous female carrying a recessive X-linked allele.

Do carriers usually show the disorder?

No, the dominant allele masks the recessive allele.

For a female to express an X-linked recessive disorder, what must occur?

She must inherit the recessive allele from both parents.

Which allele is dominant for colour blindness inheritance?

Xᴺ (normal vision).

Which allele is recessive?

Xⁿ (colour blindness).

What genotype gives a female normal vision?

XᴺXᴺ.

What genotype gives a female carrier status?

XᴺXⁿ.

What genotype gives a female colour blindness?

XⁿXⁿ.

What genotype gives a male normal vision?

XᴺY.

What genotype gives a male colour blindness?

XⁿY.

Why can males express colour blindness with only one recessive allele?

They have only one X chromosome.

What is a pedigree chart?

A diagram showing how a trait is inherited through generations.

What can pedigree charts show?

Whether a trait is dominant, recessive, autosomal, or sex-linked.

What shape represents females?

Circles.

What shape represents males?

Squares.

What do filled symbols represent?

Individuals with the condition.

What do empty symbols represent?

Individuals without the condition.

What does a half-shaded symbol represent?

An unaffected carrier.

How are individuals identified in pedigrees?

By generation and position (e.g., II4).

What suggests a dominant trait in a pedigree?

Someone is affected in every generation.

What suggests a recessive trait in a pedigree?

The trait can skip generations.

What often indicates an X-linked trait?

More males than females are affected.

What often indicates an autosomal trait?

Males and females are affected equally.

If unaffected parents have an affected child, what does this suggest?

The trait is recessive.

If unaffected parents have an autosomal recessive child, what are the parents likely to be?

Heterozygous carriers.

What is a mutation?

A change in DNA sequence or chromosome structure/number.

What are the two broad categories of mutations?

Gene mutations and chromosome mutations.

What is a gene mutation?

A change in the nucleotide sequence of a gene.

What is a chromosome mutation?

A change in chromosome structure or number.

Can mutations be beneficial?

Yes.

Can mutations be harmful?

Yes.

Can mutations have no effect?

Yes, they may be neutral.

What is a beneficial mutation?

A mutation that provides an advantage or useful variation.

What is a detrimental mutation?

A mutation that reduces normal function.

What is a neutral mutation?

A mutation with no significant effect on phenotype.

What usually causes chromosome mutations?

Errors during cell division.

What is a duplication mutation?

Part of a chromosome is copied twice.

What is a deletion mutation?

Part of a chromosome is lost.

What is an inversion mutation?

A chromosome segment is reversed.

What is a translocation mutation?

Segments are exchanged between chromosomes.

What is aneuploidy?

Having one chromosome too many or too few.

What is Trisomy 21?

Down syndrome; three copies of chromosome 21.

What is Edwards syndrome?

Three copies of chromosome 18.

What is Patau syndrome?

Three copies of chromosome 13.

What causes Cri-du-chat syndrome?

A deletion on chromosome 5.

What causes Turner syndrome?

Missing all or part of one X chromosome in females.

What causes Klinefelter syndrome?

One or more extra X chromosomes in males.

What causes XYY syndrome?

An extra Y chromosome in males.