Inheritance

Question 1

What is the definition of gene?

Answer 1

• a sequence of nucleotides along a length of DNA that codes for a particular polypeptide or protein

Question 2

What is the definition of locus (plural = loci)?

Answer 2

• position of a gene on a chromosome

Question 3

What is the definition of allele?

Answer 3

• an alternative form of a gene, due to mutations

Question 4

What is the definition of homologous chromosomes?

Answer 4

• pair of chromosomes that carry the same genes but not necessarily the same alleles

Question 5

What do eukaryotic cells have as a result of homologous chromosomes?

Answer 5

• 2 copies of every gene present in an individual = allows there to be diff. allele combinations within an individual

Question 6

What is the definition of genotype?

Answer 6

• the genetic constitution of an organism (describes all alleles an organism has)

Question 7

What is the definition of phenotype?

Answer 7

• characteristics of an organism resulting from the expression of its genotype + the envi.

Question 8

What is the definition of homozygous?

Answer 8

• when alleles of a particular gene are identical

Question 9

What is the definition of heterozygous?

Answer 9

• when alleles of a particular gene are different

Question 10

What is the definition of dominant alleles?

Answer 10

• allele that will always be expressed in phenotype (bc only needs 1 copy of the dominant allele)

Question 11

What is the definition of recessive alleles?

Answer 11

• allele expressed in phenotype if no dominant allele is present (needs 2 copies of the recessive allele)

Question 12

What is the definition of co-dominant alleles?

Answer 12

• when both alleles are equally dominant, so both contribute to, + are expressed in the phenotype

Question 13

What is the definition of an F(filial)1 generation?

Answer 13

• when a homozygous dominant individual is crossed w a homozygous recessive individual to produce all heterozygous offspring

Question 14

What is the definition of an F(filial)2 generation?

Answer 14

• offspring produced when 2 individuals from the F1 generation are crossed

Question 15

What can a test cross be used for?

Answer 15

• to find out genotype of an individual expressing a dominant phenotype
  
  • by crossing individual w another individual (2) expressing the recessive phenotype = phenotypes of offspring allows genotype of individual to be suggested
  • if any offspring expresses recessive phenotype, individual must have heterozygous genotype

Question 16

What are the 2 types of linkage in genetics?

Answer 16

• sex linkage
• autosomal linkage

Question 17

What is the definition of a sex linkage?

Answer 17

• a gene whose locus is present on only 1 sex chromosome (usually X chromosome bc is longer)

Question 18

What is the definition of an autosomal linkage?

Answer 18

• genes located on the same chromosome that don’t assort independently during meiosis so are likely to be inherited together
• occurs on autosomes: not sex chromosomes

Question 19

What is the definition of a monohybrid cross?

Answer 19

• a cross in which the alleles of just 1 gene are involved

Question 20

How do you set out a genetic diagram for a monohybrid or dihybrid cross?

Answer 20

• parental phenotype:
• parental genotype:
• gametes (drawn in circle):
• punnett square showing offspring (F1) genotypes (label male + female gametes):
• predicted ratio of phenotypes in offspring:

Question 21

How is co-dominance notated?

Answer 21

• using a capital letter for the gene w superscript letters for the alleles (e.g.l^Al^B)

Question 22

How is sex linkage notated?

Answer 22

• using a capital letter to represent chromosome (X or Y) + a subscript letter to represent the allele (e.g. X^allele)

Question 23

What are the 3 genotypes for females?

Answer 23

• X^AX^A = unaffected
• X^AX^a = carrier
• X^aX^a = affected

Question 24

What are the 2 genotypes for males?

Answer 24

• X^AY = unaffected
• X^aY = affected

Question 25

What are **multiple alleles** + why are they important?

Answer 25

- when there is **more than 2 alleles** of a gene within a pop. - creates many **genotype combinations**, leading to many diff. **phenotypes** + hence lots of **variation** in a pop. = inc. survival chances of a species, esp. if envi. conditions change

Question 26

Why do results from genetic crosses often **differ** from predicted results?

Answer 26

- bc predicted **genotypes** that genetic diagrams produce are all **based on chance** - due to **random fusion of gametes**

Question 27

What is the definition of a **dihybrid cross**?

Answer 27

- genetic cross involving the **alleles of 2 genes** at the **same time**

Question 28

What is the **ratio** for the phenotypes of offspring in a **dihybrid** cross if both the parents are **heterozygous**?

Answer 28

- 9:3:3:1

Question 29

What two factors affect the **ratio of predicted gametes** in a punnet square?

Answer 29

- autosomal linkage - crossing over in meiosis

Question 30

How does **crossing over in meiosis** affect the **ratio of predicted gametes** in a punnett square?

Answer 30

- results in **new combinations of alleles** in the **gametes** so predicted ratio of gametes may differ

Question 31

How does **autosomal linkage** effect the **predicted ratio of gametes** in a punnett square?

Answer 31

- **alleles**, for each gene linked on same chromosome, will be **inherited together** so **less combinations of alleles** in gametes so ratio of **predicted gametes** may differ

Question 32

Why does the **NO° of actual phenotypes differ** from the NO° of predicted phenotypes even when there’s **autosomal linkage**?

Answer 32

- bc **crossing over** may have occurred during **meiosis** making **new combinations of gametes** - the **further apart** the loci of 2 genes on the same chromosome are, the **more likely** crossing over takes place

Question 33

What is the definition of **epistasis**?

Answer 33

- when 1 gene **affects or masks the expression** of another in the phenotype

Question 34

What is **dihybrid inheritance**?

Answer 34

- when **2 diff. genes** determining 2 diff. characteristics are both inherited

Question 35

What are the **effects** of **epistasis**?

Answer 35

- unexpected phenotype ratios

Question 36

What is the Chi-squared test?

Answer 36

- a statistical test used when investigating differences between frequencies (observed + expected results in an experiment) in categorical data

Question 37

What is the equation for Chi-squared?

Answer 37

χ2 = Σ (O - E)^2 / E - O: observed value - E: expected value

Question 38

What is a null hypothesis?

Answer 38

- claim that there will be no sig. difference between the observed + expected values + that any difference is due to chance

Question 39

How do you calculate the degrees of freedom (df)?

Answer 39

df = n - 1 - n = NO° of categories

Question 40

What conclusions can be made when comparing the chi-squared value to the critical value?

Answer 40

- if χ2 value is > critical value, there’s <5% probability results are due to chance - so null hypothesis can be rejected bc there’s a sig. difference between observed + expected results - if χ2 value is < critical value, there’s >5% probability results are due to chance - so null hypothesis can be accepted bc there’s no sig. difference between observed + expected results

Question 41

What are the possible phenotypes + genotypes of blood groups in humans?

Answer 41

- blood group A: I^AI^A or I^AI^O - blood group B: I^BI^B or I^BI^O - blood group AB: I^AI^B - blood group O: I^OI^O

Question 42

What are the blood group of humans determined by?

Answer 42

- shape of antigens on surface of red blood cells

Question 43

How is sex determined genetically?

Answer 43

- by combination of sex chromosomes inherited from parents - females have XX chromosomes so individual must inherit a X from female parent - males have XY chromosomes so if individual inherits X chromosome from male parent = female, if it inherits Y chromosome = male