CH7/8 - Genetics, meiosis, genotype, phenotype Flashcards
nucleotide
a phosphate group, deoxyribose sugar, a nitrogen base containing either adenine, thymine, guanine, or cytosine
gene
gene
a section of DNA that
carries the code to make a protein
genome
the complete set of
DNA contained within an
organism’s chromosomes
allele
alternate forms of a gene
haploid
describes a single set
of chromosomes (n)
phenotype
the observable trait of
an individual
what is a chromosome?
Chromosomes are molecules of DNA tightly wrapped around histones made of proteins and nucleic acids. Their role is to carry genetic information. ( Chromosomes vary in size due to the number of varying nucleotides ).
Human cells contain
46 chromosomes and have a diploid number of 2n = 46.
what is an autosome?
Any chromosome (1-22) in humans that is not a sex chromosome determines mist phenotypic characteristics ( not sex )
what is a gamete?
a reproductive cell which arises from germline cells and contain half the genetic i=material of a somatic cell
diploid
having two sets (2n) of each chromosome from each parent.
homologous pair
Each has the same gene in the same order but there may be variation, resulting in different alleles.
heterogametic sex
Two different sex chromosomes ( XY = males )
homogametic sex
Two of the same sex chromosomes ( XX = females )
karyotype
Visual representation of an individual entire genome organised into homologous pairs. Usually used to check for genetic abnormalities
eg. down syndrome
aneuploidy
when a cell or organisms varies in the usual number of chromosomes,
genome
the complete set of dna contained withing an organisms dna
meiosis
A specialised form of cell division where a sing cell divides twice and forms four unique daughter cells. It is essential for sexual reproduction.
- each cell (sperm and egg) contain one copy of each chromosome which fuse together to create two copies of each chromosome.
Involves Meiosis I and meiosis II
zygote
zygote
Diploid cells are formed by the fusion of two haploid gametes
meiosis 1
Interphase: Cell grows and duplicates all. of its chromosomes in preparation for division. Identical to mitosis this happens before.
Prophase II: Nuclear membrane breaks down as chromosomes condense and line up in homologous pairs. This is important for the crossing over of genetic material.
Metaphase I: Homologous chromosomes will then line up randomly on opposite sides of the metaphase plate, with one copy (paternal or maternal) on each side. Each chromosome us attached to the microtubules.
Anaphase I: homologous chromosomes are moved apart towards opposite poles of the cell. for now, sister chromatids remain attached at the centromere
Telophase I: Nuclear membrane is cleared when chromosomes arrive at opposite sides of the cell and cleavage furrow forms.
what is crossing over?
The exchanging of genetic material from one homologue to the other during prophase I. The swap over part of their DNA at the point of chiasma
independent assortment
Random orientation of chromosomes in the middle. Each pair line up differently, irrespective of the orientation of the other homologous pair.
meiosis II
Prophase II: The two cells prepare, nuclear membranes break down, chromosomes condense, and spindle fibres form to pull the chromatids apart.
Metaphase II: Each chromosome lines up along the metaphasal plates of the cell, and microtubules form the opposite sides of the cell and prepare to pull chromatids apart.
Anaphase II: Sister chromatids are pulled towards opposite poles of the cell y the microtubules that are attached at the centromere.
Telophase II: With individual chromatids now at each pole of the cell, separate nuclear membranes begin o form around each set, and chromosomes decondense.
Cytokinesis: Splits each of the chromosome sats at opposite ends of the cell into four new individual cells. (haploid daughter cells )
Homozygous
Identical alleles for the same gene on hoologous chromosomes. Eg. (RR) ( rr)
heterozygous
having different alleles for the same gene on a homologous chromosome. Eg. (Rr)
dominant allele
The variant of a gene that masks the effect of a recessive allele of the same gene on a homologous chromosome.
recessive allele
The variant of a gene that is masked by the dominant allele on a homologous chromosome.
genotype
genetic composition of an organism at one particular gene locus
phenotype
physical or biochemical characteristics of an organism as a result of gene expression or the environment.
complete dominance
a pattern of dominance where only the dominant allele from the genotype from a heterozygous individual is expressed.
co-dominance
a pattern of dominance where both alleles from a heterozygous individual are dominant are expressed in the phenotype
incomplete dominance
a pattern of dominance where neither allele from a heterozygous individual is dominant and both traits are expresse in the phenotype.
proportionate heritability
the amount of phneotypic variance that can be explained by the genes in a given population
epigenetics
changes to an organisms phenotype resulting form modifications to gene expression form exposure to environments (e.g. sin colour changing as a result of sun exposure)
gene expression
the process of reading information stored within a gene to create a functional product, typically protein. (Eg. environmental signals are translated into biochemical changes inside a cell that lead to increased or decreased gene expression
2 steps of epigenetics
- transcription- involves reading and copying out a gene sequence from a dna molecule. this “copy” of the gene (mRNA) then moves out of the nucleus to ribosomes in the cytosol or on the rough ER for translation
- translation- involves mRNA instructing the ribosome how to build the specific protein for which the DNA sequence codes
when do epigenetic changes happen
changes ccur after transcription, they are caused by molecules that either increase or decrease the amount of transcription, therefore altering the quality of protein produced.
epigenetic methylation
DNA methylationMethyl groups attach to specific nucleotides within the DNA sequence of a certain gene, altering the level of gene expression. This usually causes the gene to go silent, decreasing the expression.
DNA demethylation is the process of removing a methyl group from the DNA sequence leading to the gene being expressed.
importance of epigenetics
Helps to control cell differentiation: even though our cells contain the same DNA they are all different. all cells propbvide specific functions, the development of these different cells is regulated by epigenetic factors which alter the rise or lowering of gene expression.
provides a mechanism for an organism to adapt and respond to ints environment ( epigenetic modifications act as a fast feedback system in which an organism can respond to it’s environment ). Eg. during hot weather, plants produces proteins which reduce heat shock, the genes for these prteoins are stimulated by high temperatures.
epigenetics across generations
- epigenetic changes can be transferred through daughter cells during meiosis
- epigenetic factors are somatically heritable, meaning they can be passed from somatic cell to somatic cell infinitely across an individuals lifespan.
linked gene
Genes are found close together on the same chromosome, meaning they have a higher chance of being inherited together. Thye can be separated during crossing over.
