U2T5 - Keywords Flashcards
Genes + Patterns of Inheritance
Gene
Short section of chromosome that codes for particular polypeptide/protein/characteristic.
Allele
Particular form of a gene.
Homozygous
Both alleles of gene are same. (TT - homozygous dominant, tt - homozygous recessive)
Heterozygous
Alleles of same gene are different. (Tt) Effect of recessive allele masked by dominant allele.
Genotype
Gene arrangement of alleles to determine particular feature.
Phenotype
Outward appearance (tall/short). Results from gene expression + interaction in environment.
Gene Locus
Position of gene on chromosome.
Haploid
Single set of unpaired chromosomes. e.g. gamete. (n)
Diploid
2 complete sets of chromosomes, one from each parent. (2n)
n
Number of chromosomes. Humans have 23 pairs so 46 chromosomes.
Homologous Chromosomes
2 similar chromosomes that each carry same genes in same locus on chromosome so each cell has 2 copies of each gene.
Mendel’s Law of Segregation
The characteristics of an organism are determined by internal factors which occur in pairs. Only 1 of a pair of such factors can be represented in a single gamete.
Monohybrid Inheritance
Inheritance of 1 characteristic (round/wrinkled)
Backcross/Test Cross
Used to determine unknown genotypes. e.g. can’t know if Tt or TT as same phenotype. Breed plant with homo recessive plant to find out which it is. If homo recessive with hetero, 1:1 ratio. If homo dom with homo recessive, all offspring hetero. Used to confirm pedigree status.
Dominant
An allele that will be more likely to be expressed, takes priority over recessive allele. Not more common though e.g. dwarfism is dom but rare.
Autosomal
Not carried on sex chromosomes. The other 22 pairs of chromosomes.
Autosomal Recessive
Not carried on sex chromosomes, only occurs when you have 2 copies of recessive allele.
Heterozygous Advantage
Disease causing alleles which in heterozygous state give selective advantage. e.g. sickle cell anaemia allows resistance to malaria + CF carriers have resistance to typhoid.
Codominance
When both alleles are expressed and neither dominates the other. e.g. when red + white flowers bred, pink flowers produced. Uppercase letter used for both alleles. Smaller letter beside it indicates allele type. e.g. RR + WW. Can have partial dominance.
Sickle Cell Anaemia
Caused by mutation altering haemoglobin structure. Faulty gene recessive + in homo rec, when o2 partial pressures low in tissues, haemo less soluble + forms crystals in cell, resulting in sickle shaped cells which can stick in narrow blood vessels causing blockage + o2 starvation. Results in early death (anaemia as lots of RBCs destroyed). Most common in Africans where malaria incidence high. If hetero, gen health good as only 40% haemo affected. Suffer mild anaemia normally but have malaria resistance.. More common in malarial places.
Lethal Allele Combinations
Abnormal ratios in offspring. e.g. sickle cell anaemia combo of 2 recessive alleles lethal. If breed 2 yellow mice, don’t get all yellow offspring. Expected ratio is 3:1 but in reality, doesn’t happen. In yellow pairs, female has dead embryos in uterus whilst if yellow + grey, few if any found. All yellow mice hetero + carry grey allele.
Dihybrid Inheritance
Inheritance of 2 characteristics. When genes on sep chromosomes, they’re unlinked.
Mendel’s Law of Independent Assortment
Each member of an allelic pair may combine randomly with either of another pair.
Multiple Alleles
Genes have more than 2 alleles that can occupy the gene locus on a pair of homologous chromosomes at any one time in any individual.
Homogametic
Females. Only produce one type of gamete, all with X.
Heterogametic
Males. Produce 2 types of gametes, half with X, half with Y. Means 50% chance of either sex at fertilisation.
Sex-Linked Characteristics
Refers to genes carried on sex chromosomes. Mainly carried on X chromosome. Hairy ears determined by sex-linked allele on Y chromosome so sons always inherit from them.
Polygenic Character
Single characteristic controlled by alleles of 2 or more genes that interact with each other. Transmitted by polygenic inheritance.
Polygenic Inheritance
The way a polygenic character is transmitted through the generations. Basis of continuous variation.
Continuous Variation
Character shows range of phenotypes with smooth graduation from one extreme to another. Many characters are polygenic. Multiple alleles could account for this but would need lots. Diff as multiple alleles at same locus + polygenic on several loci.
Hermaphrodite
Xxy
Non segregation of sex chromosomes during meiosis.
Haemophilia
Caused by recessive gene mutation which prevents formation of protein involved in blood clotting, leads to prolonged bleeding in those affected.
Discontinuous Variation
Mendel used characters to show this. Form discrete groups of characteristics, rather than continuous variation. Pea plant height discontinuous so only one gene involved.
Epistasis
1 gene modifies/masks action of another gene. 2 diff genes both affect same characteristic, can give rise to unusual ratios in genetic crosses. These genes at diff loci.
Chi-squared test
To find out if offspring characteristic nums fit expected ratio. Statistical test used when data consists of discrete variables. Compares observed with expected. Diff is deviation from expected. If significant deviation, not due to chance alone. Null Hypothesis used.
Null Hypothesis
Observed frequencies compared with expected frequencies based on this during chi-squared test. Prediction that assumes no signif diff between observed + expected ratios. Normally stated at start of stat test which it then proves or disproves.
Degrees of freedom
Need value for this to know where to read probability table. If monohybrid cross, will be 2 classes. Calculated by counting num of classes + subtracting 1 from this total so there is 1 in this case. If dihybrid, 4 classes so 3 degrees. Prob table then read at row corresponding to num of degrees of freedom to where X2 num fits.
Gene Interaction
Interaction between multiple genes that impacts phenotype.
Agouti
Greyish pattern formed on mice by bands of alternating pigment in each hair.
Genetics
Science of heredity, now characteristics pass throughout the generations.
Gregor Mendel
Started the study of genetics with his experiments on pea plants. Was a monk in Czech Republic. Studied inheritance of characteristics.
Pure Breeding
Homozygous for a particular trait.
Progeny
Offspring
Recessive
Dominated by dominant allele. Only shows in phenotype if there are 2 recessive alleles for the particular trait.
Pedigree Charts
Used to show inheritance of trait through generations. Males are squares. Females are circles. Shading indicates the occurrence of the trait being studied.
Huntington’s Disease
Autosomal dominant so can’t skip a generation.
Autosomal Dominant
Can’t pass on condition without at least one person having trait. Both males and females get it.
X-linked recessive
More common in males.
X-linked Dominant
Affects both males and females equally.
