Genetics
Think about this…. “My parents have brown eyes, why are mine blue?” “My brother is tall. Why am I short?” “Why does my sister have blonde hair while mine is brown?”
Are these inherited traits? Your eye color Your hair color and texture Your height
Are these inherited traits? Your personality Your musical, athletic, and artistic abilities
Gregor Mendel Born in 1822 in Austria Studied the garden pea plant to determine genetics Father of Genetics
Gregor Mendel Heredity – the passing on of characteristics from parents to offspring Characteristics that are inherited are called traits
Gregor Mendel Mendel studied only 1 trait at a time to control the variable The tall plants that he worked with had been tall for many generation and had always produced tall offspring This is called true breeding
Mendel’s Monohybrid Crosses Mono = one A hybrid is the offspring of parents that have different forms of a trait Such as tall and short
Mendel’s Monohybrid Crosses P generation - parents The F1 generation (hybrids) were all purple – self pollinated F2 generation had a ratio of 3:1 3 purple 1 white F stands for filial – son or daughter
The rule of dominance The dominant trait is the trait that is observed The recessive trait is the trait that ‘disappears’ What trait is dominant?
The rule of dominance Which is dominant and which is recessive? TT Tt tt BB bb Bb ww WW Ww HH hh Hh
Phenotypes and Genotypes The way an organism looks or behaves is called its phenotype
Phenotypes and Genotypes The allele combination an organism contains is its genotype represented as TT for tallness Any plant that is tall has a genotype either TT of Tt
Homozygous Homo: same Two alleles for the trait are the same (TT or tt) Which ones are homozygous?
Heterozygous Hetero = different Two alleles differ from one another (Tt)
Monohybrid crosses A a AA Aa aa Aa x Aa A: White fur a: Brown fur a cross that shows the possible offspring for one trait Punnett Square Aa x Aa A a AA Aa aa A: White fur a: Brown fur Genotypic Ratio: 1:2:1 Phenotype: 3 white:1 brown
Practice! Cross a HOMOZYGOUS dominant female rabbit with a HETEROZYGOUS male rabbit using the same trait. A: White fur a: Brown Fur A a What is the genotypic ratio? After this slide you should do the Genetics Overview and Genetics Problems #1. What is the phenotypic ratio?
Practice! Cross a HOMOZYGOUS dominant female rabbit with a HETEROZYGOUS male rabbit using the same trait. A a What is the genotypic ratio? AA AA 2 = AA 2 = Aa 2:2 or 50% After this slide you should do the Genetics Overview and Genetics Problems #1. What is the phenotypic ratio? Aa Aa 4 white fur
Practice!! Cross a female (Tt) with a male (Tt) using the traits: T: tall t: short T t T t
Practice!! Cross a female (Tt) with a male (Tt) using the traits: T: tall t: short T t T T Tt tt T t
Now its time for more practice…
Dihybrid crosses two traits calculated :RrYy x RrYy
Dihybrid Crosses: a cross that shows the possible offspring for two traits BbRr x BbRr BR bR br Br BBRR BbRR BbRr BBRr BBrr Bbrr bbRR bbRr bbrr Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth BbRr x BbRr Phenotypic Ratio: 9:3:3:1
More Complex Patterns of Heredity Codominance/ Incomplete dominance Multiple Alleles Sex-Linked Traits
Codominance: two dominant alleles are expressed at the same time CRCR CWCW CRCW
Codominance Sickle-Cell Anemia is another codominant trait. NSNA NSNA NA=Normal RBC NANA NANA NS=Sickle Cell RBC NA
Multiple Alleles: traits with more than 2 alleles Blood type has 3 alleles: A, B, O A and B are codominant over O O is recessive Phenotype Genotype Can Receive From Can Donate To A AA, AO A, O A, AB B BB, BO B, O B, AB AB A, B, AB,O O OO A, B, AB, O
What are Sex-Linked Traits? Traits that are located on one of the sex chromosomes (XY) Hemophilia: Failure of blood to clot Alix and Nicholas II Muscular Dystrophy: wasting away of muscles
Can I inherit a sex-linked disease? Mothers (XX) can pass disorders to both sons (XY) and daughters (XX) Fathers (XY) can only pass disorders to daughters (XX) In humans, the term sex-linked traits usually refers to X-linked traits. The human X-chromosome is much larger than the Y. Thus, there are more X-linked than Y-linked traits. Most X-linked genes have no homologous loci on the Y chromosome. Most genes on the Y chromosome not only have no X counterparts, but they encode traits found only in males (e.g. testis- determining factor). Examples of sex-linked traits in humans are color blindness and hemophilia. Fathers pass X-linked alleles to only and all of their daughters. Males receive their X chromosome only from their mothers. Fathers cannot, therefore, pass sex-linked traits to their sons. Mothers can pass sex-linked alleles to both sons and daughters. Females receive two X-chromosomes, one from each parent. Mothers pass on one X-chromosome (either the maternal or paternal homologue) to every daughter and son. Most disorders are carried on the X chromosome, so males are more likely to inherit them.
How can I tell if I have a genetic disorder? Karyotypes are a “map” of all 46 (23 pair) of chromosomes.
What’s wrong with this Karyotype? Is this a male or a female?
What’s wrong with this Karyotype? Is this a male or a female?
Down Syndrome Down syndrome occurs because of the presence of an extra 21st chromosome. Down syndrome is also called trisomy 21 Physical Traits Short stature. A child often grows slowly and, as an adult, is shorter than average. A short, wide neck with excess fat and skin Small, low-set ears.
Klinefelter Syndrome chromosome abnormality that affects only men born with at least one extra X chromosome. The male with Klinefelter Syndrome will be born with 47 chromosomes in each cell, rather than the normal number of 46. Klinefelter Syndrome is also called 47 X-X-Y syndrome. An infant with Kleinnfelter's Syndrome appears normal at birth, but the defect usually becomes apparent in puberty when secondary sexual characteristics fail to develop, and testicular changes occur that eventually result in infertility in the majority of those affected.
Patau syndrome Trisomy 13 Most cases of Patau syndrome are not inherited, but occur as random events during the formation of reproductive cells (eggs and sperm). Symptoms: Mental & motor challenged polydactyly (extra digits) Heart defects Cleft palate Spinal defects