Genetics

Question 1

Genetics is

Answer 1

A fields of biology that studies heredity and genes in living organisms

Question 2

Heredity

Answer 2

Is the passing of traits/genes from the parents to their offspring (either through sexual or
asexual reproduction).

Question 3

Gene

Answer 3

A segment of 𝐷𝑁𝐴 encoding one trait (one protein). It is the heritable traits that can be
passed from parent to offspring. It is also the basic unity of heredity.
- Genes are coded for 𝐷𝑁𝐴 and located in specific regions on chromosomes.

• Genes tell cells how to make proteins.
• One strand of 𝐷𝑁𝐴 can have many genes, all which give instruction for how to make and
  operate the body.
• Children inherit their biological parent’s gens that express specific traits (like physical
  characteristics, natural talents and genetic disorders).

Question 4

Locus

Answer 4

A segment of 𝐷𝑁𝐴 containing more than one gene; a region of chromosome.

Question 5

Chromosomes

Answer 5

Tread like structure found in the nucleus and composed of 𝐷𝑁𝐴 and proteins. It contains the cell’s genetic information. Every human cell contains 23 pairs of homologous
chromosomes.

• One pair called sex chromosome that define the sex of the human being (𝑋𝑌 – male. 𝑋𝑋 – female.)
• 22 pairs that are called autosomal chromosomes.

Question 6

Homologous chromosomes

Answer 6

Rwo chromosome of the same pair, similar in shape and size. They encode to the same traits, but not necessarily identical. One paternal and one maternal.

Question 7

Allele

Answer 7

An alternative form of the same gene. Coding for particular trait. Found on a locus on the
homologous chromosome.

• E.g. the alleles of eye colours are blue, brown etc…

Question 8

Karyotype

Answer 8

The number and appearance of chromosome in the cell’s nucleus.

Question 9

Genome

Answer 9

The entire genomic information of an organism.

Question 10

Genotype

Answer 10

Sum of all the alleles of a trait in an individual, whether they are expressed or not.

Question 11

Phenotype

Answer 11

Describes the observed physical appearance of an individual. Determined both by
makeup and environment influence.

Question 12

Mendelian Genetics

Answer 12

The inheritance of chromosomes in conducted through meiosis where gametes are formed. Gametes are 
haploid cells (contain one set of chromosomes). 

• Diploid – Cells that contain two complete sets of chromosomes (2𝑁).
• Haploid cells have half the number of chromosomes (𝑁).

Question 13

Gregor Mendel

Answer 13

Gregor Mendel was a scientist and a monk in the 19th century who lived in Brno, Czech Republic. He
developed several laws regarding genetic based on his work of crossbreeding different types of pea plants.

Question 14

Mendel’s laws of genetics

Answer 14

1. Law of Segregation: principles of Dominance and Monohybrid Cross.
2. Law of Independent Assortments: Dihybrid Cross.

Question 15

Monohybrid cross

Answer 15

A cross in which only one trait (allele) is being studied, involves parents with different alleles (contrasting genotypes and phenotypes). The parent generation (𝑃 generation), refers to the individuals being crossed. The offspring are the filial (𝐹 generation). 𝐹1 and 𝐹2revers to the multiple generations.

• 𝐹2 Genotypes – 1:2:1 (1PP:2Pp:1pp).
• 𝐹2 Phenotypes – 3:1(3 ping: 1 white).

Question 16

Law of Independent Assortment

Answer 16

Genes assort independently of one another during gamete production. Genes of different assort independently of one another during gamete production (crossing over).

Question 17

Dihybrid cross

Answer 17

A cross in which two traits (genes) are being studied, involves parents with different alleles
at two different loci (contrasting genotypes and phenotypes).
* 𝐹2 Phenotypes – 9:3:3:1.

Question 18

Codominance

Answer 18

A condition when two dominants are expressed, like in blood type: both 𝐴 and 𝐵 are dominating alleles, and so in heterozygotes carrying both 𝐴 and B, we get 𝐴𝐵 blood type.

Question 19

Mitochondrial Inheritance

Answer 19

The inheritance of a trait encoded in the mitochondrial genome. Because of the oddities of mitochondria,
mitochondrial inheritance does not obey the classic rules of genetics.
Persons with a mitochondrial disease may be male or female but they are always related in the maternal line and no male with the disease can
transmit it to his children.

Question 20

Sex-linked Inheritance

Answer 20

Sex-linked inheritance patterns differ from autosomal patterns due to the fact that the chromosomes aren’t paired in males (𝑋𝑌). This leads to the expression of sex-linked traits being predominantly associated
with a particularly gender.

As human females have two 𝑋 chromosomes (and therefore two alleles), they can be either homozygous or heterozygous. Hence, 𝑋-linked dominant traits are more common in females (as either allele may be
dominant and cause disease).

Human males have only one 𝑋 chromosome (and therefore only one allele) and are hemizygote for 𝑋linked traits. 𝑋-linked recessive traits are more common in males, as the condition cannot be masked by a
second allele.

Question 21

The following trends always hold true for X−linked conditions:

Answer 21

• Only females can be carriers (a heterozygote for a recessive disease condition), males cannot be
  heterozygous carriers.
• Males will always inherit an 𝑋-linked trait from their mother (they inherit a 𝑌 chromosome from
  their father).
• Females cannot inherit an 𝑋-linked recessive condition from an unaffected father (must receive
  his dominant allele).