CH11TheBasicPrinciplesofHereditypart-03 - LINKED ALLELES DO...

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Unformatted text preview: LINKED ALLELES DO NOT ASSORT INDEPENDENTLY Linkage is The Tendency of genes on The same chromosome (linked genes) To be inheriTed TogeTher Bva X bbw (2 poinT TesT cross) -Body: Gray (B) or Black (b) -Wings: Normal (V) or VesTigeal (v) GameTes produced if loci for TraiTs is unlinked F1 of BBVV X bbw “5' Gray. normaiwmgs .' " 4 .a I W ' ' E3va ParenTaI—Type gameTes RecombinanT—Type gameTes ED 1% Black. vestigial wings bbvv ExpecTed resulTs wiTh independenT assorTmenT AC'l'LlCll resulTs - independenT assorTmenT does Gray. Black. Gray. Black, normal vestigial vestigial normal I @190 . _. Bb W bbw 575 5?5 575 575 965 944 206 185 noT apply if loci are close TogeTher on same c‘some Linked gene are groups of genes on The same chromosome ThaT do NOT assorT independenle '2 q in 1 I. '- m c' I. v b 85!, Two homologous Chromosomes undelgo synapsas in meiOSlS 1 G' CFDSSiflg'OUEI belwean :I paar of homologous {none-star) CthflléIldS / Meiosis I \ Figure 11-12 p 247 Crossing over can lead To recombinaTion of linked genes - genes locaTed farTher aparT are more likely To be separaTed Than genes closer TogeTher RecombinaTion is The appearance of new gene combinaTions and is caused by: - Crossing over ' IndependenT assorTrnenT V V v v SI ID BI In - - Main-ms ll ' - V. I V v I I v B - ' D B ' ' D Pamnlal Hocomblnanl Fiecornbinanl Palenlal type type typo type Four haploid cells produced - ParenTal Types are idenTical To The gameTes produced by The P generaTion - RecombinanT Types have new combinaTions of alleles SEX CHROMOSOMES DETERMINE SEX in MAMMALS ° Autosomes are chromosomes #1-22 'tha't do not determine sex ' 56X chromosomes — chromosome #2 3, X or Y chromosome Female karyotype: 22 pairs of autosome + XX Male ka ryotype: 22 pairs of autosome + XV at :i i ii it it it 9i a? we a! we 38 HHHHHHHH In a; ti it I g qI 9. Every egg cell contains 22 autosomes and an X c’some A sperm cell contains 22 autosomes and either an X or aY c’some k FE Es —" —r- K X (a 3: a: 2% 13 1!: l'! 19 4 a s r: l I 21 2'2 X ‘f Y c’some is smaller Sperm determines sex of offspring in mammals 1 § ' s\ FEMALE lithe egg is fertilized by an X sperm, the zygote will contain two X chromosomes and the offspring will be female. MALE It the egg is fertilized by a Y sperm, the zygote will contain an XY combination and the offspring will be male. X-LINKED GENES HAVE UNUSUAL INHERITANCE PATTERNS .2 X-linked genes are genes for traits unrelated to sex determination found only on X c'some - Fig 11-16 Color—blind male Heterozygous lemaie Normal male x0 v x0 x9 x0 v Hemizygous Carrier males have onlyl * copy of x—Iinl-(ed genes inherited XC Gamales )(c from mother »- - ~ / \t i .: l\. t.) Gametes \c_// \. Garnetes Colo r-blind male X9 Y ta) To be color-blind, a female must inherit alleles for color blindness from both parents. Heterozygous female x0 x9 Carrier — heterozygous mother who doesn't have the disorder but donates mutant recessive allele to 1/2 of her offspring 1 x0 Gametes xc If. . _ . ._\ . ‘\ ‘t [\JI \5u Normal lomale Normal female x5 x0 xc xc I I I I Carrier Normal male Color-blind male :03 r KG Y I Normal color vision I Color-blind {lo} If a normal male mates With a carrier {hetero- zygous} female, belt of their sons watjid be expected to be color-blind and half of their daughters would be EXPECTEEl ['0 be CEIHIEFS. X INACTIVATION - BARR BODIES in FEMALES ' A Barr body is a condensed/inactive X chromosome in the cells of female mammal (Figure 11-17 p 251) Barr body (inactivated l chromosome) 1 o The zygote and early embryonic cells have two X chromosomes. one From each parent. 0 Random inactivation of one X chromosome occurs early in development. Roughly half the cells inactivate one X chromosome (left cell), and the other half inactivate the second X chromosome (right cell). The inactive X chromosome is visible as a Barr body near the nuclear envelope 0 Chromosome inactivation persists through subsequent mitotic divisions. resulting in patches of cells in the adult body. Variegation 7 females that are heterozygous for genes on the X chromosome have cells which express different phenotypes eg. calico cat (a) Inactivation of one X chromosome in female cells, 11 ...
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CH11TheBasicPrinciplesofHereditypart-03 - LINKED ALLELES DO...

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