Leaving Cert Biology Genetics, DNA & Evolution: (a) (i) What is meant by the ter

Question

(a) (i) What is meant by the term heredity?

Passing on (or transmission) of characteristics (traits or genes) from one generation (or cell) to the next.

(ii) State Mendel's Law of Independent Assortment (2nd Law).

Each member of one pair of alleles can combine randomly with either member of another pair (at gamete formation) OR Members of another pair of factors (alleles) separate independently.

(b) The series of images below represents the four main stages of the DNA profiling technique invented by Sir Alec Jeffreys in 1984.

1. Sample used to create a DNA profile
2. A DNA profile

(i) Distinguish between DNA profiling and genetic screening.
(DNA Profiling: Generating a pattern of bands from a (DNA) sample; Genetic screening: Test to show presence (or absence) of a gene.)

(ii) Explain each of the Stages 1, 4 of DNA profiling shown above.
Stage 1: DNA is isolated (or extracted or released)
Stage 2: DNA (strands are) cut (into fragments using enzymes)
Stage 3: Fragments are separated on the basis of size
Stage 4: (The pattern) is analysed (or compared or examined).

(iii) Give any two applications of DNA profiling.
Forensic (or example)
Medical (or example)

(iv) Identify twins have the same DNA profile. Explain why this is so.
(Both) have same genotype (for same genes) or (both) come from same zygote (fertilised egg).

(c) In Andalusian chickens the allele for black feathers (B) exhibits incomplete dominance over the allele for white feathers (b). When a black, homozygous rooster (male) is crossed with a white, homozygous hen (female) all the newly hatched chicks will have an intermediate phenotype of speckled color (Bb) known as "blue".

(i) Explain the terms underlined in the passage above.
Allele: A version (variant) of a gene or alternative form of a gene.
Incomplete dominance: When both alleles are expressed or heterozygous condition is intermediate.
Homozygous: (When) identical alleles are present (for a trait).
Phenotype: The (physical) expression of a gene or genotype.

(ii) Determine all the possible genotypes and phenotypes of the offspring of a cross between the following chickens:
"blue" rooster X "blue" hen
Include in your answer the ratio of the resulting phenotypes.
Offspring Genotypes: BB, Bb, bb
Offspring Phenotypes: Black, Blue (or speckled), White
Ratio of Offspring Phenotypes: 1 Black: 2 Blue: 1 White

(iii) What would be the effect on the offspring phenotype ratio, in the genetic cross (ii) above, if there was no incomplete dominance between the two alleles for feather color, and if black feather was the dominant trait and white feather was the recessive trait?

(a) (i) What is meant by the term heredity? Passing on (or transmission) of characteristics (traits or genes) from one generation (or cell) to the next - Leaving Cert Biology - Question 12 - 2020

Worked Solution & Example Answer:(a) (i) What is meant by the term heredity? Passing on (or transmission) of characteristics (traits or genes) from one generation (or cell) to the next - Leaving Cert Biology - Question 12 - 2020

What is meant by the term heredity?

State Mendel's Law of Independent Assortment (2nd Law).

Distinguish between DNA profiling and genetic screening.

Explain each of the Stages 1, 4 of DNA profiling.

Give any two applications of DNA profiling.

Identify twins have the same DNA profile. Explain why this is so.

Explain the terms underlined in the passage above.

Determine all the possible genotypes and phenotypes of the offspring of a cross between the following chickens: "blue" rooster X "blue" hen.

What would be the effect on the offspring phenotype ratio, in the genetic cross (ii) above, if there was no incomplete dominance.

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