BISC 100 - Lecture 26 & 27: Genetics


Flashcards on BISC 100 - Lecture 26 & 27: Genetics, created by Chelsi Souch on 10/08/2016.
Chelsi Souch
Flashcards by Chelsi Souch, updated more than 1 year ago
Chelsi Souch
Created by Chelsi Souch over 7 years ago

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Question Answer
Heredity transmission of traits
Genetics scientific study of heredity
Mendel created - purebred (what does that mean?) varieties of pea plants and – crossed two different purebred varieties.
Hybrids are the offspring of two different purebred varieties. – The parental plants are the P generation. – Their hybrid offspring are the F1 generation. – A cross between the F1 plants forms the F2 generation. – F stands for “filial”
character heritable feature that varies among individuals
A trait variant of a character.
The seven characters studied by Mendel
Tracking one character (flower color)
Mendel’s four hypotheses (1 & 2) 1. The alternative versions of genes are called alleles (previously termed traits). Example: Gene for flower color - P allele = purple color - p allele = white color 2. For each inherited character, an organism inherits two alleles, one from each parent. – An organism is homozygous (pure breeding or true breeding) for that gene if both alleles are identical. – An organism is heterozygous for that gene if the alleles are different (Hybrid). – Example: Flower color (P = purple; p = white) » PP and pp = homozygous » Pp = heterozygous
Mendel’s four hypotheses (3 & 4) 3. If two alleles of an inherited pair differ, – then one determines the organism’ s appearance is called the dominant allele and – the other has no noticeable effect on the organism’ s appearance and is called the recessive allele. – Example: Flower color in pea plants » P = dominant allele (purple color) » p = recessive allele (white color) » PP and Pp = purple flower; pp = white flower 4. Gametes (haploid) carry only one allele for each inherited character. – The two alleles for a character segregate (separate) from each inherited character. – The two alleles for a character segregate (separate) from each other during the production of gametes. – This statement is called the law of segregation. – Example: Flower color (P = purple; p = white) » PP parent produces only P gametes » Pp parent produces P or p gametes » pp parent produces only p gametes
1. Mendel’s Law of Segregation That organisms have two genetic elements which separate when gametes are formed. The fusion of gametes at fertilization pairs these elements once again Occurs during meiosis I: homologous chromosomes separation in anaphase I
2. Mendel’s Law of Independent Assortment Factors for different characteristics (different gene pairs) are inherited independently from one another Occurs during meiosis I: Independent assortment of homologous chromosomes in metaphase 1
What is a Dihybrid cross?
Incomplete dominance MANY ALLELES SHOW INCOMPLETE DOMINANCE In monohybrid crosses in some cases outcome was different Ex 1. SNAPDRAGONS (red X white = PINK)
Codominance Both alleles express together in the heterozygotes
Epistasis One gene may alter the effect of (expression) of another gene Ex 1. Mice have TWO GENES fur coat colour B and C B = BLACK b = brown C = COLOUR If cc (homozygous recessive) is present the mouse will be white regardless of which B gene it has One gene may alter the effect of (expression)of another gene
Environment Can modify the expression of the gene Coat colour of animals Can modify the expression of the gene
Polygeneic inheritance Most characteristics are determined more than one gene Height and Skin color
Pleiotropy and sickle cell disease – Pleiotropy is when one gene influences several characters. – Sickle-cell disease exhibits pleiotropy • results in abnormal hemoglobin proteins, and causes disk-shaped red blood cells to deform into a sickle shape with jagged edges. • causes multiple symptoms: weakness, pain, organ damage and paralysis
Multiple alleles Many genes have more than two alleles in the population – In a population Multiple alleles often exist for a characteristic
Human ABO blood groups are an example of multiple alleles and codominance Blood cells have either A or B type surface carbohydrates, or none (O) • The immune system produces blood proteins called antibodies that bind to foreign carbohydrates. • If a donor’ s blood cells have a carbohydrate (A or B) that is foreign to the recipient, the blood cells may clump together, potentially killing the recipient. – The clumping reaction is the basis of a blood-typing lab test. – The human blood type alleles IA and IB are codominant, with both alleles expressed in heterozygous individuals who have type AB blood.
Multiple alleles for the ABO blood groups Alleles are alternative forms of a gene that arose by mutation. Each gene (100s or 1000s of base pairs long) can have multiple alleles.
Sex chromosomes and sex-linked genes Sex chromosomes influence the inheritance of certain traits. Human sex chromosomes: XX = female; XY = male
genetic abnormality rare version of an inherited trait
genetic disorder nherited condition that causes medical problems
Inheritance patterns in humans are often studied by tracking inheritance patterns of genetic disorders through generations
Pedigree is a chart showing the pattern of inheritance of a trait in a family
Syndrome The set of symptoms that characterize a genetic disorder
Any gene located on a sex chromosome is called sex-linked gene. • Most sex-linked genes are found on the X chromosome. • Red-green colorblindness is a common human sex-linked disorder and caused by a malfunction of light-sensitive cells in the eyes
Sex-linked traits
HYPERTRICHOSIS Severe hypertrichosis is quite rare, almost certainly due to unknown genetic defects, and can result in excessive or animal-like hair on both face and body. Unfortunately, some of these people have been displayed in carnival sideshows with names such as "dog-boy" or the "bearded lady."
Linked genes Linked genes are located close together on a chromosome and tend to be inherited together. – Thomas Hunt Morgan (early 1900s) • used the fruit fly Drosophila melanogaster and • determined that some genes were linked based on the inheritance patterns of their traits. • Example: Body color gene and wing length gene are linked
Genetic recombination: crossing over Crossing over can – separate linked alleles, – produce recombinant gametes with new combinations of alleles, and – produce offspring with recombinant phenotypes. • The percentage of recombinant offspring among the total is called the recombination frequency. Crossing over can produce recombinant gametes
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