Biology - Chapter 7 GENETICS

Genetics

DNA

Deoxyribonucleic Acid

Purpose of DNA

Stores genetic information essential for the growth, development, and functioning of living organisms.

Nucleotide

Building blocks of DNA, consisting of a sugar, phosphate group, and a nitrogenous base.

Gene

A section of DNA that has a specific order of bases which codes a protein.

Complementary Base Pairs

Adenine and Thymine, Cytosine and Guanine

Double Helix

structure of DNA formed by two intertwined strands of nucleotides.

Allele

Different forms of a gene (because of differences in the base sequences)

Genotype

The combination of alleles inherited for a specific trait. E.g. Rr

Phenotype

The observable characteristics or traits of an organism.

E.g. brown eyes

Homozygous

Alleles for the gene are the same. E.g. BB or bb

Heterozygous

Alleles for the gene are different E.g. Bb

Homozygous dominant

E.g. BB, where both alleles are dominant.

Homozygous recessive

E.g. bb, where both alleles are recessive.

Number of chromosomes in an individual

46 (23 pairs)

Diploid

Cells that have 2 complete sets of chromosomes.

E.g. skin cell

Haploid

Cell with one one set of chromosomes.

E.g sperm or egg cell

Telomere

Repetitive base sequences to protect the ends of chromosomes and DNA

Homologous chromosomes

pairs of chromosomes that have the same size, length and same genes at the same location.

Number of autosomes in an individual

44 (22 pairs)

Number of sex chromosomes in an individual

2 (1 pair)

Sex chromosomes for a female

xx

Sex chromosomes for a male

xy

How many homologous pairs do females have compared to males?

Females have 23 pairs, males have 22 pairs

Aneuploidy

Describes an incorrect number of chromosomes in an individual.

Monosomy

One missing chromosome E.g. Turner’s Syndrome

Trisomy

One extra chromosome E.g. Down’s Syndrome

Polyploidy

An organism’s has more than two sets of each chromosome.

Codominance

Both alleles from the genotype are fully expressed in the phenotype of the heterozygous individual. E.g. C^rC^w (flowers with both white and red petals).

Incomplete dominance

Neither allele from the genotype is fully expressed, resulting in a ‘blending’ of traits.

Sex-linked genes

Genes located on sex chromosomes that are not related to biological sex.

Genome

All the genetic information that is contained in the cell or species

Karyotypes

A photograph of a person’s chromosomes