Genes and inheritance

Question 1

Define a gene

Answer 1

gene as a unit of inheritance

Question 2

distinguish gene and allele

Answer 2

Gene: a length of DNA that codes for a polypeptide, with a specific sequence of nucleotides as part of a DNA molecule.
Allele: variant forms of genes (1 or more alternative sequences of a single gene locus)

Question 3

Locus

Answer 3

position on chromosomes where a gene occurs.

Question 4

Dominant, recessive

Answer 4

Dominant: an allele with a phenotype that is expressed even when present with an allele that is recessive to it
Recessive: an allele with a phenotype that is not expressed when present with an allele that is dominant to it.

Question 5

Homozygous/heterozygous

Answer 5

Homozygous: A genotype in which the 2 alleles of a gene are the same
Heterozygous: …different

Question 6

Phenotype

Answer 6

the way in which the genotype of an organism is expressed

Question 7

Genotype

Answer 7

the alleles that an organism carries, present in every cell.

Question 8

Explain why observed ratios often differ from expected ratios, especially when there are small numbers of progeny.

Answer 8

The probability calculated will apply to each individual independently, so we may not get expected ratio, especially with a small sample size of progeny.
(must be large: 4000)

Question 9

Explain how genotype is linked to phenotype

Answer 9

Each allele from each parent has an equal chance of being passed onto offspring. 2 alleles of genes in each cell form the genotype of an organism.
One allele is dominant over the other allele, and expresses itself in both homozygous and heterozygous conditions, expressing the organism’s phenotype.

Question 10

carrier

Answer 10

A carrier is an individual who possesses the recessive allele but appear normal phenotypically.

Question 11

how genes are inherited from one generation to the next generation via the gametes.

Answer 11

In sexual reproduction, haploid gametes are formed by meiosis
At fertilisation, male and female gametes fuse to form a zygote
Zygote, a diploid cell, has 2 sets of chromosomes, one homologous pair from each parent
2 alleles of each gene present in the new individual

Question 12

Use genetic diagrams to solve problems..

Answer 12

Key: Let N be dominant trait
Let n be recessive trait

Parental/F(Filial)1 generation:
Phenotype: normal x disease
Genotype: Nn x nn
Gametes(circled): N n x n n

F1/F2 generation:

Normal (Nn)
D  gametes    N       n (circled)
I   (random 
S  fertilisation)
E    n             Nn      nn
A
S    n             Nn      nn
E   (circled)
(Nn)

F1/F2 generation:
Genotypic ratio: 1Nn: 1nn
Phenotypic ratio: 1normal: 1 disease

NOTE: Repeat EXACTLY what qn end says.

Question 13

expected ratios

Answer 13

Simple crosses have expected ratios of genotype: 3:1 and phenotype: 1:2:1

Question 14

Monohybrid cross

Answer 14

investigation of single contrasting characteristic.

Question 15

Test cross and result

Answer 15

breeding mystery individual with homozygous recessive individual
If there are any recessive offspring, mystery parent is heterozygous

Question 16

Mono/di-hybrid Test cross

Answer 16

Monohybrid test cross: 1:1

Dihybrid test cross: 1:1:1:1

Question 17

Law of segregation

Answer 17

During meiosis, pairs of alleles separate so that each cell has one allele of a pair. Allele pairs separate independently during the formation of gametes.

Question 18

Law of independent assortment

Answer 18

During meiosis, the separation of one pair of alleles is independent of the separation of another pair of alleles.

Question 19

Calculate Chance: multiple offspring produced

Answer 19

independent chance: try 2 times of ¼ chance= ¼ *¼ = 1/16 chance

Question 20

Pedigree

Answer 20

family tree that enables us to trace the transfer of a specific genetic trait through several generations

Question 21

Sex, blood type and colour genotypes

Answer 21

Sex: XY (male), XX (female) X^H,X^h
Blood type: I^A,I^B, i
Colour: C^RC^W

Question 22

Codominance, Incomplete dominance, Multiple alleles and examples

Answer 22

Codominance: alleles that are both expressed in a heterozygous organism (IAIB)
Incomplete dominance: phenotype of F1 hybrid is between the phenotypes of the 2 parental varieties (Colours(pink): CRCW)
Multiple alleles: 3 or more alleles occupy the same locus. (IA,IB, i)

Question 23

describe Sex-linked inheritance

Answer 23

Due to genes present on the sex chromosomes

Question 24

Autosomal chromosome

Answer 24

non sex chromosome

Question 25

How pedigree shows it is Sex-linked?

Answer 25

Only males are affected and females are carriers.

Question 26

Why Only males are affected and females are carriers.

Answer 26

(disease) caused by recessive allele linked to X chromosome. Male descendants only carry 1 X chromosome, increasing their chances of inheriting the disease from their ancestors. Females have 2 X chromosomes, so a single recessive allele on the X chromosome will not result in disease.

Question 27

Codominance:

For 2 parents with different genotypes to produce (hetero/homo) dominant offspring:

Answer 27

1 parent must be heterozygous to pass on recessive allele (i) to offspring (for the homozygous parent to pass on dominant allele to have single dominant offspring).

Question 28

Codminance:

For recessive offspring:

Answer 28

Both parents must have recessive alleles to pass in in gametes to produce recessive offspring

Question 29

Discontinuous variation:

Answer 29

one or more discrete (pheno/geno) types with no intermediate forms, genetically determined, not affected by environmental factors

Question 30

Continuous variation

Answer 30

environmental and genetic factors