Lesson 17: Patterns of Inheritance blackwellpublishing.com Roots: Di = 2 mono = 1 Homo = same Hetero = different Hemo = blood

Gregor Mendel Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas – used good experimental design – used mathematical analysis collected data & counted them – excellent example of scientific method

Pollen transferred from white flower to stigma of purple flower anthers removed all purple flowers result Mendel’s work Bred pea plants – cross-pollinate true breeding parents – raised seed & then observed traits – allowed offspring to self-pollinate & observed next generation ? self-pollinate

Mendel collected data for 7 pea traits Each trait is represented by a specific allele on a specific chromosome. Allele = genes that determine a specific trait.

2 nd generation 3:1 75% purple-flower peas 25% white-flower peas Parents 100% 1 st generation (hybrids) 100% purple-flower peas X true-breeding purple-flower peas true-breeding white-flower peas self-pollinate

What did Mendel’s findings mean? Some traits mask others – purple & white flower colors are separate traits that do not blend purple x white ≠ light purple purple masked white – dominant allele functional protein – affects characteristic masks other alleles – recessive allele no noticeable effect allele makes a non-functioning protein homologous chromosomes allele producing functional protein mutant allele malfunctioning protein mygenetic.wordpress.com

Genotype vs. phenotype Difference between how an organism “looks” & its genetics – phenotype Form of the trait that gets expressed “what you see” – genotype An organism’s actual alleles Explain Mendel’s results using …dominant & recessive …phenotype & genotype F1F1 P X purplewhite all purple

Inheritance of genes On the chromosomes passed from Mom & Dad to offspring are genes – may be same information – may be different information eye color (blue or brown?) eye color (blue or brown?)

Remember how Meiosis separates the alleles into sex cells? This separation is called the Law of Segregation. palaeos.com

Effect of genes Genes come in different versions – brown vs. blue eyes – brown vs. blonde hair – Alleles = different forms of a gene

Homozygous = same Heterozygous = different Homozygous = same Heterozygous = different Homozygous dominant = AA Homozygous recessive = aa Heterozygous = Aa Tt Bb Ww Yy rr RR Aa AB Ss bb Ee BB aa XY

Genes affect how you look… X BB bb Bb Where did the blue eyes go??

X Bb bb Bb bb Why did the blue eyes stay??

X Bb BB or Bb bb Where did the blue eyes come from??

Genes come in “versions” – brown vs. blue eye color – Alleles (different forms of a gene) Alleles are inherited separately from each parent – brown & blue eye colors are separate & do not blend either have brown or blue eyes, not a blend Some alleles mask others – brown eye color masked blue

How does this work? eye color (brown?) hair color eye color (blue?) Paired chromosomes have same kind of genes – but may be different alleles

Traits are inherited as separate units 1 from Mom 1 from Dad For each trait, an organism inherits 2 copies of a gene, 1 from each parent – a diploid organism inherits 1 set of chromosomes from each parent diploid = 2 sets (copies) of chromosomes homologous chromosomes

Making gametes BB= brown eyes bb= blues eyes Bb= brown eyes BBbbBbBb  brown is dominant over blue  blue is recessive to brown Remember meiosis! B B b b B b Dominant = can mask others Recessive = can be hidden by others

How do we say it? BB= brown eyes bb= blues eyes Bb= brown eyes 2 of the same alleles Homozygous 2 different Heterozygous BB B B bb b b BbBb B b homozygous dominant homozygous recessive

Punnett squares Bb x Bb male / sperm female / eggs X BB BbBbbb BbBb B b Bb

Genetics vs. appearance There can be a difference between how an organism looks & its genetics – appearance or trait = phenotype brown eyes vs. blue eyes – genetic makeup = genotype BB, Bb, bb 2 people can have the same appearance but have different genetics: BB vs Bb

Genetics vs. appearance vs. eye color (brown) eye color (brown) BB B B eye color (blue) eye color (brown) Bb B b How were these brown eyes made?

Making crosses Can represent alleles as letters – flower color alleles  P or p – true-breeding purple-flower peas  PP – true-breeding white-flower peas  pp PP x pp PpPp F1F1 P X purplewhite all purple

Punnett squares Pp x Pp Pp male / sperm P p female / eggs PP 75% 25% 3:1 25% 50% 25% 1:2:1 % genotype % phenotype PPPpPp PpPppp PpPp PpPp 1 st generation (hybrids) Aaaaah, phenotype & genotype can have different ratios

Beyond Mendel’s Laws of Inheritance

Extending Mendelian genetics Mendel worked with a simple system – peas are genetically simple – most traits are controlled by single gene – each gene has only 2 version 1 completely dominant (A) 1 recessive (a) But its usually not that simple! mac122.icu.ac.jp

Incomplete dominance Hybrids have “in-between” appearance – RR = red flowers – rr = white flowers – Rr = pink flowers make 50% less color RRRrrr  RR  WW  RW

Incomplete dominance true-breeding red flowers true-breeding white flowers X P 100% 100% pink flowers 1 st generation (hybrids) self-pollinate 25% white 2 nd generation 25% red 1:2:1 50% pink

Incomplete dominance RW x RW RW male / sperm R W female / eggs 25% 1:2:1 25% 50% 25% 1:2:1 % genotype % phenotype RR RW WW 25% 50%

Codominance Equal dominance – Chickens A black-feathered chicken is crossed with a white- feathered chicken. All of the babies are white with black speckling. Both white and black show up equally. x = /echotig8.files.wordpress.com

More Codominance… x /z.about.com

Multiple Alleles More than one allele to select from. – Blood “types” can be A, B, AB, or O. – The alleles to make these types include A, B and i. – “i” is the recessive allele and A and B are both dominant. – So to get… Type A you must have AA or Ai Type B you must have BB or Bi Type AB you must have AB Type O you must have ii

BLOOD Blood cells have antigens and antibodies. Antigens are tiny receptors on the outside of the blood cell that matches the “type.” Antibodies are what the cell doesn’t like (which is anything different from the “type.”) Multiple Alleles

Blood Types A A A Type A B B B Type B Type O A B A Type AB B Antigens (none) Anti-B Anti-A none Anti-A and B Multiple Alleles

Genetics of Blood type pheno- type genotype antigen on RBC antibodies in blood donation status AA A or A i type A antigens on surface of RBC anti-B antibodies __ BBB or B i type B antigens on surface of RBC anti-A antibodies __ AB both type A & type B antigens on surface of RBC no antibodies universal recipient Oi ii i no antigens on surface of RBC anti-A & anti-B antibodies universal donor Multiple Alleles

One gene : Many effects The genes that we have covered so far affect only one trait But most genes are affect many traits – 1 gene affects more than 1 trait dwarfism (achondroplasia) gigantism (acromegaly) dymaxionweb.com/mentalfloss.cachefly.net

Acromegaly: André the Giant lat34.com

AA  Aa x aa Inheritance pattern of Achondroplasia aa A a Aa A a Aa x Aa Aa aa Aa 50% dwarf:50% normal or 1:1 aa Aa 67% dwarf:33% normal or 2:1 Aa library.thinkquest.org

Many genes : One trait Polygenic inheritance – additive effects of many genes – humans skin color height weight eye color intelligence behaviors Polygenic = “many genes”

Human skin color AaBbCc x AaBbCc – range of shades – most children = intermediate skin color – some can be very light & very dark Polygenic = “many genes”

Albinism Johnny & Edgar Winter albino Africans melanin = universal brown color cnb.uam.es xenophilius.files.wordpress.com theglenblog.blogspot.com Albinism is the absence of pigment.

Coat color in other animals 2 genes: E,e and B,b – color (E) or no color (e) – how dark color will be: black (B) or brown (b) E–B– E–bb eeB–eebb

Environment effect on genes Phenotype is controlled by both environment & genes Coat color in arctic fox influenced by heat sensitive alleles s3.amazonaws.com Color of Hydrangea flowers is influenced by soil pH / /images.pictureshunt.com Human skin color is influenced by both genetics & environmental conditions wxyc.org

SEX and GENES Women & men are very different, but just a few genes create that difference In mammals = 2 sex chromosomes – X & Y – 2 X chromosomes = female: XX – X & Y chromosome = male: XY XY XX

Sex chromosomes

Sex-linked traits Sex chromosomes have other genes on them, too – especially the X chromosome – hemophilia in humans blood doesn’t clot – Duchenne muscular dystrophy in humans loss of muscle control – red-green color blindness see green & red as shades of grey XY XX

XHXH Y male / sperm XHXH XhXh female / eggs XHXHXHXH XHXhXHXh XHYXHYXhYXhY XHXhXHXh XHXH XhXh XHYXHY Y XHXH XHXHXHXH XHYXHY XHXhXHXh XhYXhY sex-linked recessive 2 normal parents, but mother is carrier HH Hh x XHYXHY XHXhXHXh

library.thinkquest.org

Most Common Allele Dominant or Recessive Because an allele is dominant does not mean… – it is better, or – it is more common Polydactyly dominant allele Either One! accessexcellence.org biocrawler.comthelastoutpost.com

Polydactyly Recessive allele far more common than dominant  only 1 individual out of 500 has more than 5 fingers/toes  so 499 out of 500 people are homozygous recessive (aa) the allele for >5 fingers/toes is DOMINANT & the allele for 5 digits is recessive individuals are born with extra fingers or toes stanford.wellsphere.com absurdintellectual.com

Hound Dog Taylor blogs.sun.com /aagallery.aadl.org mevio.com