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Biology midterm 2 .docx

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BIOL 1500
Tanya Da Sylva

Heterozygous: an individual inherits two different forms of the same gene Homozygous: an individual inherits the same allele from both parents; genes are the same. Dominant allele: where the phenotype is always present. Recessive allele: can be masked but is still present Difference between an organism’s genotype and its phenotype? Genotype: the organism’s actual genes that you cannot completely see. Phenotype: the physical appearance of organisms. Single gene trait: a single gene with two alleles and each one produces a distinct phenotype. Mendel’s contribution to genetics: -Law of segregation and law of independent assortment Segregation: two factors/ traits from each parent separate and go to the offspring so the offspring will carry both genes. Law of independent assortment: Laws of chance decide which traits the offspring will have Dihybrid crossing. How the law of independent assortment relates to dihybrid crossing? -Green pod colour and yellow seed colour (dominant) -Yellow pod colour and green seed colour (recessive) -Offspring was heterozygous (GgYy) (green pod and yellow seed) Chromosome theory of inheritance: explains that chromosomes carry genetic material. Inheritance patterns may be explained by assuming that genes are located on specific sites of the chromosomes. (e.g. Blonde hair and blue eyes usually go together because hair and eye colour are located on the chromosome closely together.) Why linked genes cannot assort independently: Linked genes are on the same chromosome so they are physically attached and cannot separate Inheritance patters in recessive and dominant traits? – If it skips a generation; it is recessive. If the child has the dominant trait one of the parents must also have it. Examples of human disorders (dominant): -Achondroplasia Marfan syndrome -Huntington Disease Examples of human disorders (recessive): -Sickle cell -Cystic fibrosis -Hemophilia -Colour-blindness Incomplete dominance: when one allele of the same gene isn’t completely dominant over the other (Red flower and White flower produce pink flower) Multiple allele: there are three or more alleles for a trait. (Blood type A, B, and O) Co-dominance: When a single gene has two dominant alleles. (Blood type AB) Pleiotropic: one gene influencing many traits (e.g. Genes that control cats fur can influence their brain and eye colour.) Polygenic: many genes affecting one trait. (e.g. Skin colour. BBBBBB= very dark skin, bbbbbb= very light skin. All other combinations are intermediates. Sex-linked inheritance: XX= female child XY= male child. Genes that are carried by either sex are called sex-linked inheritance. Sex-linked diseases: diseases determined by a chromosome. -Hemophilia: an X chromosome disease; usually affecting males. -Chromosomal abnormalities: Any change in normal structure of chromosome; resulting in physical or mental abnormalities. -Turner’s Syndrome: Chromosomal disorder affecting females who have only one X chromosome; dwarfism, heart problems, underdeveloped sex organs. How can sickle-cell be adaptive?: It can protect against malaria. Darwin’s Observation about natural selection: -All species have great fertility potential -Populations remain stable in size -Environmental resources are limited -Individuals of a population vary in inheritance. -Much variation is inheritable Why individuals cannot evolve: They cannot change their own genetics. Populations can evolve. Not humans. Why evolution doesn’t lead to perfectly adapted organisms---mutations and changes happen all the time. Not all of the less adapted organisms result in killing another. How evolutionary change takes place? -Mutation -Natural selection -Evolutionary lineage -Sexual recombination Difference between natural selection and evolution? Evolution: A change into something different or better Natural selection: Where individuals do not survive or reproduce and do not pass on their genes Examples of natural selection: -Some giraffes have long necks and some have short necks. If short tree shrub
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