unit 2 AOS 1 genetics glossary Flashcards
cell
the basic unit of all iving things
nucleus
the ‘control center’ of the cell found in all eukaryote cells. It contains the instructions for the metabolism of the cell, its growth and division - the place where the codes to build proteins (genes) are located.
chromosomes
a strand of DNA found all living things, usually in the nucleus. All species have different numbers of chromosomes.
DNA
Deoxyribonucleic acid. It carries the code, and all the instructions for inheritance. It is made up of a sugar (deoxyribose), a phosphate group and four nitrogen bases (adenine, guanine, cytosine and thymine). It is arranged in a double helix and has a slightly negative charge.
autosome
Chromosomes are not involved in sex determination. Humans have two copies of each of the 22 different types of autosomes (44 in total.)
sex chromosomes
chromosomes involved in the determination. Humans have two of these - one large chromosome X and a smaller Y. Normal females have two X chromosomes, a normal male has an X an Y.
Karyotypes
is the complete set of chromsomes in an organism, arranged and displayed in a systematic way.
homologous chromosomes
A pair of matching chromosomes containing the same genes, one of maternal origin and one of paternal origin.
trisomy
three copies of a chromosome. Occurs as the result of faulty cell division at meiosis to form gametes. Down’s syndrome is also called trisomy
somatic cell
body cell, contains two sets of chromosomes
mitosis
cell division in somatic cells for growth and repair. One diploid parent cell produces two identical diploid daughter cells.
diploid
two sets of chromosomes - one maternal and one paternal in origin
meiosis
cell division in gonads to produce gametes. One diploid parent cell produces four non-identical haploid daughter cells called gametes for reproduction.
gonad
a general term for ovaries (female) and testes (male)
gamete
a general name for a ova or egg (female) and sperm (male)
haploid
one complete set of chromosomes. Gametes are the only haploid cells in humans
zygote
a new cell produced by the fusion of ovum and sperm cells - fertilisation
gene
a section of DNA along chromosomes that codes for one inherited trait. A gene is found on at a particular chromosome at a particular place or locus.
allele
one version of a gene. One gene can have a number of different alleles that may exist at the same locus. Each individual carries 2 copies of each autosome and so 2 alleles - which may be the same or different. A gene located on the X chromosome is not found on the Y: therefore males only get one allele for an X - linked gene
mutation
a change in DNA sequence for an allele caused by exposure to radiation or some chemicals. May be spontaneous. Mutations in gametes do not affect the individual producing them BUT can be passed down to the next subsequent generations. Mutations in somatic cells don’t get passed on.
locus (loci)
the position on a specific chromosome where a gene is located
genotype
the actual set of alleles for a gene present in an individual
phenotype
the outwards, physical expression of an individual - it is the end result of the interaction between the genotype and the environment.
environment
all factors affecting the growth and life of an individual - nutrition, light etc.
homozygous
both alleles for the genotype are identical e.g. BB YY
heterozygous
both alleles in the genotype are different e.g. Bb Yy
hybrid
another term for heterozygous often used on animals or plants
pure breeding
another term for homozygous often used on animals or plants
dominant allele
a trait is always expressed in the phenotype regardless if the individual is homozygous or heterozygous for a trait. Denoted by a capital letter in the genotype
recessive allele
a trait is only expressed in the phenotype if it is the only allele present - i.e. homozygous. Denoted by a lower letter in the genotype.
genome
the complete collection of DNA in an organism.
the function of a chromosome
chromosomes carry genetic info in the form of genes, sequences of DNA that encode proteins and regulate cellular functions.
ensuring the accurate transmission of genetic material during cell division.
arrangement of chromosomes
organized into homologous pairs. Each pair consists of one chromosome from each parent, carrying the same set of genes although allele may differ.
chromosome structure
The double helix structure is composed of DNA and associated proteins, the DNA is wrapped in histones, forming nucleosomes.
each chromosome consists of two sister chromatids connected at a centromere
karyotype
is the complete set of chromosomes in an organism, arranged and displayed in a systematic way
how karyotypes are paired
due to size, shape and banding pattern
function of karyotes
to analyse the number and structure of chromosomes in an organism, helping to detect chromosomal abnormalities.
how many diploid chromosomes are in humans
46 in their somatic ( body ) cells
aneuploidy
chromosomal abnormality where an organism possesses an incorrect number of total chromosomes caused by the addition or loss of an individual chromosomes
monosomy
if an organism has one missing chromosome
trisomy
if an organism has one extra chromosome
tetrasomy
if an organism has two extra chromosomes
poly ploidy
if an organism has more than 2 sets of extra chromosomes
Distinction Between Genome, Gene, and Allele
- Genome: The complete set of genetic material in an organism, including all of its chromosomes and genes.
- Gene: A segment of DNA that codes for a specific protein or function. It is a unit of heredity.
- Allele: Different versions or variants of a gene that arise from mutations. Each individual has two alleles for each gene, one inherited from each parent.
Distinction Between Autosome and Sex Chromosome
- Autosome: Chromosomes that are not involved in determining the sex of an individual. Humans have 22 pairs of autosomes.
- Sex Chromosome: Chromosomes that determine the sex of an individual. In humans, these are the X and Y chromosomes. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
Nature of a Homologous Pair of Chromosomes
are pair of chromosomes, one inherited from each parent, that carry genes for the same traits at the same loci (positions). They may have different alleles for these genes.
Presentation of an Organism’s Set of Chromosomes as a Karyotype
Karyotype: A complete set of chromosomes in an organism arranged and displayed in pairs, usually by size and shape. It is used to study chromosomal abnormalities and the chromosomal composition of an organism.
Using Karyotypes to Diagnose Chromosomal Abnormalities
Karyotype Analysis: By examining the number, size, and shape of chromosomes, karyotyping can identify abnormalities such as extra chromosomes (e.g., Down syndrome) or structural changes (e.g., deletions, duplications).
How Meiosis Produces Haploid Gametes from Diploid Cells
Meiosis: A type of cell division that reduces the chromosome number by half, resulting in four haploid gametes (sperm or eggs) from one diploid cell. This process involves two rounds of division (Meiosis I and Meiosis II) and ensures genetic variation.
Significance of Crossing Over and Independent Assortment
- Crossing Over: The exchange of genetic material between homologous chromosomes during meiosis, increasing genetic diversity by creating new allele combinations.
- Independent Assortment: The random distribution of homologous chromosome pairs into gametes during meiosis, contributing to genetic variation.
Distinction Between Dominant and Recessive Phenotypes
- Dominant Phenotype: Expressed when at least one dominant allele is present (e.g., A_).
- Recessive Phenotype: Expressed only when two recessive alleles are present (e.g., aa). The dominant allele masks the effect of the recessive allele.
why is independent assortment important
Independent assortment ensures that the two alleles of every gene are separated from one another during meiosis,1so as to produce new combinations of alleles during anaphase I and increase genetic variations within a population
