Inheritance

Question 1

What are alleles?

Answer 1

Alleles: alternative forms of the same gene

Question 2

What is an autosome?

Answer 2

Autosome: a chromosome not involved in sex determination (human genome has 22 pair’s autosomes and 1 pair of sex chromosomes)

Question 3

What are chromosomes?

Answer 3

Chromosomes: the self-replicating genetic structures of the cell containing the DNA

Question 4

What are codominant alleles?

Answer 4

Alleles whose effects both show in the phenotype of a heterozygote
(Remember incomplete dominance is where we get a blending of characteristics, breeding a red and white flower gives pink flowers, co-dominance both characteristics are expressed so we would get flowers with red and white spots)

Question 5

What is a dominant allelle?

Answer 5

Dominant allele: an allele whose effect always shows in the phenotype when it is present, it is the allele expressed in the heterozygous state

Question 6

What is a gene pool?

Answer 6

All the alleles of all the genes in a population of organism, which results in variation

Question 7

What is the genotype of an organism?

Answer 7

Genotype: the alleles of a gene (genetic constitution) an individual inherits

Question 8

What does haploid mean?

Answer 8

Haploid: a nucleus with only a single set of chromosomes

Question 9

What are heterosomes?

Answer 9

Heterosomes: chromosomes involved in sex determination which are different in appearance. In humans that Y chromosome determining male sex characteristics is much shorter than the X.

Question 10

What does heterozygous mean?

Answer 10

Heterozygous: Possessing different alleles of genes at one or more loci on homologous chromosomes

Question 11

What does heterogametic sex produce?

Answer 11

Heterogametic sex: the sex that produces gametes containing sex chromosomes of two types. Males produce gametes with either an X or Y in them

Question 12

What does homogametic sex produce?

Answer 12

Homogametic sex: the sex that produces gametes containing sex chromosomes of the same type. Female gametes all have X chromosome

Question 13

What are homologous chromosomes?

Answer 13

Homologous chromosomes: a pair of chromosomes containing the same gene sequences each derived from one parent

Question 14

What does homozygous mean?

Answer 14

Homozygous (pure breed): possessing the same alleles of genes at one or more loci on homologous chromosomes

Question 15

What is the locus on a chromosome?

Answer 15

Locus: the position on a chromosome of a gene or other chromosome marker

Question 16

What are multiple alleles and give an example?

Answer 16

Multiple alleles: genes that have more than two different alleles
Blood groups

Question 17

What is phenotype?

Answer 17

Phenotype: the features of an individual that result from the expression of the genes and their interaction with the environment

Question 18

What is a recessive allele?

Answer 18

Recessive allele: an allele whose effects only show when there are no dominant alleles present. ( ie you need 2 copies for it to be expressed) A recessive phenotype is always homozygous. The allele not expressed in the heterozygous state

Question 19

What are sex chromosomes?

Answer 19

Sex chromosomes: the X and Y chromosomes in human beings which determine the sex of an individual
Beware not all males are XY and females XX!!!

Question 20

What is sex linkage?

Answer 20

Sex linkage: genes, other than those that determine sexual features, which occupy a locus on one sex chromosome but not the other

Question 21

What is a test cross? Explain how it works (4)

Answer 21

Test-cross: cross fertilisation carried out between an unknown genotype showing the dominant phenotype and an individual showing the recessive phenotype. (ie rr)

Test cross: you can see a phenotype but not the genotype. If a person shows the recessive trait, they must be homozygous for the characteristic, but showing a dominant trait they could be homozygous or heterozygous. You can find out which by breeding the unknown with the homozygous recessive.
If all the results are dominant, then the parent is likely to be homozygous dominant. There may be some doubt as it is possible that the random nature of fertilisation has just resulted in the dominant allele being passed on, so a large offspring number can help increase the certainty.
If the results are mixed then the parent must be heterozygous

Question 22

When looking at the multiple alleles of blood groups which are dominant and recessive?

Answer 22

IA, IB are codominant whilst IO is recessive.

Question 23

What is a monohybrid cross?

Answer 23

Monohybrid crosses: A simple breeding experiment involving a single characteristic

Question 24

What are genes and what do they code for?

Answer 24

Genes are lengths of DNA that code for proteins. It is the proteins that control phenotype as enzymes, pumps and hormones and structural elements

Question 25

Explain how the “weedy Y” makes a difference in sex linked traits.

Answer 25

The Y chromosomes is small, containing few genes and does little else than determine sex. The X chromosomes is large and contains 1000s of genes. Females have 2 X chromosomes whilst males only have 1 copy, so the inheritance of the genes on the X chromosome is different for males and females, hence this inheritance is sex linked.

Question 26

What is the difference between codominance and incomplete dominance?

Answer 26

With co-dominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together.

With incomplete dominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits.