Chapter 9 Fundamentals of Genetics Genetics- the branch of biology that studies how traits are transmitted from parents to offspring Gregor Mendel 1822-1884

Section 1 Mendel’s Legacy Heredity- the transmission of characteristics from parents to offspring Mendel studied 7 traits in pea plants: Plant height (tall, short) Flower position (axial, terminal) Pod color (green, yellow) Pod appearance (smooth, constricted) Seed texture (round, wrinkled) Seed color (yellow, green) Flower color (purple, white) Trait-a contrasting form of a hereditary characteristic

Mendel’s Methods 1st: allowed plants to self-pollinate in order to produce true- breeding plants 2nd: cross- pollinated plants that were true-breeding for contrasting traits (he called these his P generation) 3rd: The results of crossing the P generation gave him his F1 generation 4th: crossed F1 offspring to produce F2 offspring

The ratio that he always got from his F1 generation was 4:0. YY x yy = all green (4:0)

The ratio that he always got in his F2 generation was 3:1 Yy x Yy = 3 green and 1 yellow (3:1)

He called the controls that determined how traits were transmitted, factors We call them “alleles” or “genes” Allele- alternative form of a gene Gene- a segment of DNA that controls a particular hereditary trait

Recessive and Dominant Traits Dominant- the allele that is expressed AA or Aa Recessive- the allele that is masked; the only way for a recessive trait to be exhibited is if 2 recessive alleles are present aa Free-dominant Dimples - dominant Attached- recessive Widow’s peak-dominant

Tongue rolling-dominant * sex-linked characteristic Tongue rolling-dominant DOMINANT TRAITS RECESSIVE TRAITS eye coloring brown eyes grey, green, hazel, blue eyes vision farsightedness normal vision normal vision normal vision normal vision nearsightedness night blindness color blindness* hair dark hair non-red hair curly hair full head of hair widow's peak blonde, light, red hair red hair straight hair baldness* normal hairline facial features dim ples unat tach ed earl obes frec kles broa d lips no dimples attached earlobes no freckles thin lips appendages extra digits fused digits short digits fingers lack 1 joint limb dwarfing clubbed thumb double-jointedness normal number normal digits normal digits normal joints normal proportion normal thumb normal joints other immunity to poison ivy normal pigmented skin normal blood clotting normal hearing normal hearing and speaking normal- no PKU susceptibility to poison ivy albinism hemophilia* congenital deafness deaf mutism phenylketonuria (PKU) Hitchhiker’s thumb-recessive Albinism-recessive

The Law of Segregation Factors separate during game formation; each gamete only receives 1 factor from every pair This occurs during meiosis

The Law of Independent Assortment Two traits, although present in a parent are not necessarily transmitted together in the offspring For example if a yellow, smooth pea is crossed with a green, wrinkled pea, will all offspring be either yellow and smooth or green and wrinkled?

No, because genes for each of those traits become separated during the formation of gametes