inheritance y13

What is a gene?

A base sequence made of DNA that determines the structure of proteins

What is an allele?

An alternative form of a gene occurring due to mutations

What is an autosome?

a chromosome that is not involved in sex determination

What are chromosomes?

Self replicating genetic structures of the cell containing DNA

What are co-dominant alleles?

Alleles whose effects show in the phenotype of a heterozygote

What is a dominant allele?

An allele whose effects show always shows In the phenotype when it is expressed in the genotype

What is a gene pool?

All the alleged of all the genes in a population of organisms

What is a genotype?

The combination of alleles of a gene that an individual inherits

What is a haploid?

A nucleus with only a single set of chromosomes

What is a homologous pair of chromosomes?

One maternal and one paternal chromosomes with the same genes at the same loci

What are heterosomes?

Chromosomes involved in sex determination that are different in appearance

What does heterozygous mean?

Possessing different alleles of genes at a locus on homologous chromosomes

What is heterogametic sex?

The sex that produced gametes containing sex chromosomes of two types

What is homogametic sex?

The sex that produces gametes containing sex chromosomes of the same type

What is meant by homozygous?

Possessing the same alleles of genes at one or more loci on homologous chromosomes

What is locus?

The position on a chromosome of a gene

What is a phenotype?

The physical features of an individual due to the expression of genes

What is a recessive allele?

An allele that is only expressed when a dominant allele isn’t present

What are the sex chromosomes?

X and Y chromosomes in humans that determine the sex of an individual

What is sex linkage?

Genes that determine sexual features that occupy a locus in one sex chromosome but not the other

What is test cross?

An experiment using the unknown genotype of one or both parents to identify the ratio in which offspring will have the characteristic

What is monohybrid crosses?

A simple breeding experiment involving one characteristic to see the individuals phenotype

What is dihybrid inheritance?

The inheritance of two characteristics that are controlled by different genes, each having different alleles

What is dihybrid crosses?

Used to show the likelihood of offspring inheriting certain combinations of the two characteristics from the parents

How do you do a dihybrid crosses question?

1. Identify the parents genotype

2. Identify the possible gamete combinations

3. Do a punnet square

4. Identify the offspring phenotypes from their genotypes

5. Work out a ratio

What is co dominance?

2 alleles are equally dominant, meaning they’re both expressed in the phenotype

• Seen when there is more than 2 alleles of a gene

What is an example of co dominance?

The blood types - A , B , AB, O

What is group A blood type?

• has anti-B antibodies

• Has A antigens

What is group B blood type?

• has anti-A antibodies

• Has B antigens

What is group AB blood type?

• Has no antibodies

• Has A and B antigens

• is a universal receiver

What is group O blood type?

• has anti-A and anti-B antibodies

• Has no antigens

• Is a universal donor

How many pairs of chromosomes do humans have?

• 23 pairs

• 22 of these pairs have homologous partners that are identical in appearance (autosomes)

• The remaining pair are the sex chromosomes

What are the sex chromosomes?

• human females → 2 X chromosomes

• Human males → one X chromosome and a smaller Y chromosome

What is the difference between the X and Y chromosome?

• X → longer and has more genes and DNA

• Y → shorter and different shape to X so less genes and chromosomes

Why does characteristics controlled by recessive alleles on the X chromosome appear more in males?

There’s no homologous portion on the Y chromosome (since it’s shorter) that may have the dominant allele that prevents the recessive allele from being expressed

What is meant by a sex linked gene?

Any 2 genes that appear on the same sex chromosome

What is autosomal linkage?

When two or more genes are carried on the same autosome

What caused autosomal linked genes in a chromosome to end up in different gametes?

Crossing over during meiosis → this is random and very rare

The closer together two genes are located on the autosome…

… the more closely they are said to be linked because crossing over is less likely to split them up

How are the genes presents on homologous chromosomes?

Capital (dominant) genes are on one chromosome

Lower case (recessive) genes are on the same chromosome