genetics and inheritance

Question 1

What is meant by a genome?

Answer 1

• (All) the DNA in a cell/organism;
• (all) the ‘genes’/alleles’ ‘genetic material/code’ in a cell/organism/ person’
• the total number of DNA bases in a cell/organism’

Question 2

What is a gene pool?

Answer 2

All the alleles in a population

Question 3

What is meant by a recessive allele?

Answer 3

*Only expressed in the homozygote / not expressed in the heterozygote / not expressed if dominant present;1

Question 4

What does Hardy Weinberg’s equation predict

Answer 4

• The frequency/proportion of alleles (of a particular gene);
• Will stay constant from one generation to the next/over generations / no genetic change over time;
• Providing no mutation/no selection/population large/population genetically isolated/mating at random/no migration

Question 5

Define gene linkage

Answer 5

(Genes/loci) on same chromosome;

Question 6

What is meant by the term phenotype

Answer 6

an expression of its genetic constitution and its interaction with the environment

Question 7

State three causes of genetic variation

Answer 7

• Mutation
• Crossing over
• Independent segregation / assortment (of homologous chromosomes)
• Random fusion of gametes / fertilisation / mating

Question 8

How do multiple alleles of a gene arise?

Answer 8

• mutations;
• which are different / at different positions in the gene;

Question 9

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.

Answer 9

• Small sample size;
• Fusion/fertilisation of gametes is random;
• Linked Genes; Sex-linkage / crossing over;
• Epistasis;
• Lethal genotypes;

Question 10

Define epistasis

Answer 10

• interaction between two genes where one allele affects/influences the expression of another

Question 11

Describe why observed phenotypes don’t match expected values

Answer 11

• Fertilisation is random
• OR
• Fusion of gametes is random;
• Small/not-large population/sample;
• Selection advantage/disadvantage/lethal alleles;

Question 12

Rules for Dominant alleles

Answer 12

• Affected offspring MUST have at least one affected parent.

• Unaffected parents ONLY have unaffected offspring.

• If both parents are affected and have an unaffected offspring, both parents must be Heterozygous

Question 13

Rules for recessive alleles

Answer 13

Unaffected parents can have an affected offspring (if they are Heterozygous)

Question 14

Male offspring are more likely than females to show recessive sex-linked characteristics. Explain why.

Answer 14

• (Recessive) allele is always expressed in males / males have one (recessive) allele;
• Females need two recessive alleles / females need to be homozygous recessive / females could have dominant and recessive alleles / be heterozygous;

Question 15

Explain how a single base substitution causes a change in the structure of a polypeptide

Answer 15

• Change in (sequence of) amino acid(s)/primary structure;
• Change in hydrogen/ionic/disulfide bonds;
• Alters tertiary/30 structure;

Question 16

define sex linkage

Answer 16

• The X chromosome carries normal body genes, and these are linked to the genes, which determine sex, so these body genes are referred to as being sex-linked genes.

Question 17

describe SEX LINK Rules

Answer 17

DADS & DAUGHTERS (Recessive)

• If a Daughter is affected (homozygous recessive)
• Her Father is NOT
• AND it is a recessive disease/characteristic
• It is NOT SEX-LINKED

MUMS & SONS (DOMINANT)

• If a Son is affected
• His Mum is NOT (homozygous recessive)
• AND it is a DOMINANT disease/characteristic
• It is NOT SEX-LINKED

Question 18

define Dihybrid Inheritance

Answer 18

• Dihybrid inheritance involves a phenotype that is inherited as the result of two different genes, thus two characteristics.

Question 19

define Autosomal linkage

Answer 19

• Autosomal chromosomes are chromosomes that are not directly involved in determining the sex of an organism.