Biology - Chapter 7 GENETICS

Genetics

DNA

Deoxyribonucleic Acid

DNA

Stores genetic information

Nucleotide

Building blocks of DNA. 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

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

Homologous pairs of females 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

When an organism has more than two sets of each chromosome

Tetrasomy

When an organism has two extra chromosomes

Codominance

Both alleles from the genotype are fully expressed in the phenotype of the heterozygous individual. E.g. C^rC^w

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